bpo-38614: Use test.support.LOOPBACK_TIMEOUT constant (GH-17554)

Replace hardcoded timeout constants in tests with LOOPBACK_TIMEOUT of
test.support, so it's easier to ajdust this timeout for all tests at
once.
diff --git a/Lib/test/test_smtplib.py b/Lib/test/test_smtplib.py
index d0c9862..a3e5b3f 100644
--- a/Lib/test/test_smtplib.py
+++ b/Lib/test/test_smtplib.py
@@ -245,7 +245,8 @@
 
     def testBasic(self):
         # connect
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         smtp.quit()
 
     def testSourceAddress(self):
@@ -253,7 +254,8 @@
         src_port = support.find_unused_port()
         try:
             smtp = smtplib.SMTP(self.host, self.port, local_hostname='localhost',
-                                timeout=3, source_address=(self.host, src_port))
+                                timeout=support.LOOPBACK_TIMEOUT,
+                                source_address=(self.host, src_port))
             self.addCleanup(smtp.close)
             self.assertEqual(smtp.source_address, (self.host, src_port))
             self.assertEqual(smtp.local_hostname, 'localhost')
@@ -264,14 +266,16 @@
             raise
 
     def testNOOP(self):
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         expected = (250, b'OK')
         self.assertEqual(smtp.noop(), expected)
         smtp.quit()
 
     def testRSET(self):
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         expected = (250, b'OK')
         self.assertEqual(smtp.rset(), expected)
@@ -279,7 +283,8 @@
 
     def testELHO(self):
         # EHLO isn't implemented in DebuggingServer
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         expected = (250, b'\nSIZE 33554432\nHELP')
         self.assertEqual(smtp.ehlo(), expected)
@@ -287,7 +292,8 @@
 
     def testEXPNNotImplemented(self):
         # EXPN isn't implemented in DebuggingServer
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         expected = (502, b'EXPN not implemented')
         smtp.putcmd('EXPN')
@@ -295,7 +301,8 @@
         smtp.quit()
 
     def testVRFY(self):
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         expected = (252, b'Cannot VRFY user, but will accept message ' + \
                          b'and attempt delivery')
@@ -306,7 +313,8 @@
     def testSecondHELO(self):
         # check that a second HELO returns a message that it's a duplicate
         # (this behavior is specific to smtpd.SMTPChannel)
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.helo()
         expected = (503, b'Duplicate HELO/EHLO')
@@ -314,7 +322,8 @@
         smtp.quit()
 
     def testHELP(self):
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         self.assertEqual(smtp.help(), b'Supported commands: EHLO HELO MAIL ' + \
                                       b'RCPT DATA RSET NOOP QUIT VRFY')
@@ -323,7 +332,8 @@
     def testSend(self):
         # connect and send mail
         m = 'A test message'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.sendmail('John', 'Sally', m)
         # XXX(nnorwitz): this test is flaky and dies with a bad file descriptor
@@ -340,7 +350,8 @@
 
     def testSendBinary(self):
         m = b'A test message'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.sendmail('John', 'Sally', m)
         # XXX (see comment in testSend)
@@ -356,7 +367,8 @@
     def testSendNeedingDotQuote(self):
         # Issue 12283
         m = '.A test\n.mes.sage.'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.sendmail('John', 'Sally', m)
         # XXX (see comment in testSend)
@@ -371,7 +383,8 @@
 
     def testSendNullSender(self):
         m = 'A test message'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.sendmail('<>', 'Sally', m)
         # XXX (see comment in testSend)
@@ -389,7 +402,8 @@
 
     def testSendMessage(self):
         m = email.mime.text.MIMEText('A test message')
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.send_message(m, from_addr='John', to_addrs='Sally')
         # XXX (see comment in testSend)
@@ -414,7 +428,8 @@
         m['To'] = 'John'
         m['CC'] = 'Sally, Fred'
         m['Bcc'] = 'John Root <root@localhost>, "Dinsdale" <warped@silly.walks.com>'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.send_message(m)
         # XXX (see comment in testSend)
@@ -448,7 +463,8 @@
         m = email.mime.text.MIMEText('A test message')
         m['From'] = 'foo@bar.com'
         m['To'] = 'John, Dinsdale'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.send_message(m)
         # XXX (see comment in testSend)
@@ -476,7 +492,8 @@
         m = email.mime.text.MIMEText('A test message')
         m['From'] = 'foo@bar.com'
         m['To'] = 'John, Dinsdale'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.send_message(m, from_addr='joe@example.com', to_addrs='foo@example.net')
         # XXX (see comment in testSend)
@@ -507,7 +524,8 @@
         m['From'] = 'Bernard, Bianca'
         m['Sender'] = 'the_rescuers@Rescue-Aid-Society.com'
         m['To'] = 'John, Dinsdale'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.send_message(m)
         # XXX (see comment in testSend)
@@ -540,7 +558,8 @@
         m['Resent-From'] = 'holy@grail.net'
         m['Resent-To'] = 'Martha <my_mom@great.cooker.com>, Jeff'
         m['Resent-Bcc'] = 'doe@losthope.net'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.send_message(m)
         # XXX (see comment in testSend)
@@ -579,7 +598,8 @@
         m['Resent-Date'] = 'Thu, 2 Jan 1970 17:42:00 +0000'
         m['Resent-To'] = 'holy@grail.net'
         m['Resent-From'] = 'Martha <my_mom@great.cooker.com>, Jeff'
-        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost',
+                            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         with self.assertRaises(ValueError):
             smtp.send_message(m)
@@ -1130,7 +1150,8 @@
 
     def test_smtputf8_NotSupportedError_if_no_server_support(self):
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.ehlo()
         self.assertTrue(smtp.does_esmtp)
@@ -1145,7 +1166,8 @@
 
     def test_send_unicode_without_SMTPUTF8(self):
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         self.assertRaises(UnicodeEncodeError, smtp.sendmail, 'Alice', 'Böb', '')
         self.assertRaises(UnicodeEncodeError, smtp.mail, 'Älice')
@@ -1158,15 +1180,16 @@
         msg['To'] = 'Dinsdale'
         msg['Subject'] = 'Nudge nudge, wink, wink \u1F609'
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         with self.assertRaises(smtplib.SMTPNotSupportedError):
             smtp.send_message(msg)
 
     def test_name_field_not_included_in_envelop_addresses(self):
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3
-        )
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
 
         message = EmailMessage()
@@ -1242,7 +1265,8 @@
 
     def test_test_server_supports_extensions(self):
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.ehlo()
         self.assertTrue(smtp.does_esmtp)
@@ -1251,7 +1275,8 @@
     def test_send_unicode_with_SMTPUTF8_via_sendmail(self):
         m = '¡a test message containing unicode!'.encode('utf-8')
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.sendmail('Jőhn', 'Sálly', m,
                       mail_options=['BODY=8BITMIME', 'SMTPUTF8'])
@@ -1265,7 +1290,8 @@
     def test_send_unicode_with_SMTPUTF8_via_low_level_API(self):
         m = '¡a test message containing unicode!'.encode('utf-8')
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         smtp.ehlo()
         self.assertEqual(
@@ -1301,7 +1327,8 @@
             oh là là, know what I mean, know what I mean?
             """)
         smtp = smtplib.SMTP(
-            HOST, self.port, local_hostname='localhost', timeout=3)
+            HOST, self.port, local_hostname='localhost',
+            timeout=support.LOOPBACK_TIMEOUT)
         self.addCleanup(smtp.close)
         self.assertEqual(smtp.send_message(msg), {})
         self.assertEqual(self.serv.last_mailfrom, 'főo@bar.com')