bpo-38614: Use default join_thread() timeout in tests (GH-17559)

Tests no longer pass a timeout value to join_thread() of
test.support: use the default join_thread() timeout instead
(SHORT_TIMEOUT constant of test.support).
diff --git a/Lib/test/test_asynchat.py b/Lib/test/test_asynchat.py
index 74041ed..ce85057 100644
--- a/Lib/test/test_asynchat.py
+++ b/Lib/test/test_asynchat.py
@@ -14,7 +14,6 @@
 
 HOST = support.HOST
 SERVER_QUIT = b'QUIT\n'
-TIMEOUT = 3.0
 
 
 class echo_server(threading.Thread):
@@ -122,7 +121,7 @@
         c.push(b"I'm not dead yet!" + term)
         c.push(SERVER_QUIT)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents, [b"hello world", b"I'm not dead yet!"])
 
@@ -153,7 +152,7 @@
         c.push(data)
         c.push(SERVER_QUIT)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents, [data[:termlen]])
 
@@ -173,7 +172,7 @@
         c.push(data)
         c.push(SERVER_QUIT)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents, [])
         self.assertEqual(c.buffer, data)
@@ -185,7 +184,7 @@
         p = asynchat.simple_producer(data+SERVER_QUIT, buffer_size=8)
         c.push_with_producer(p)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents, [b"hello world", b"I'm not dead yet!"])
 
@@ -195,7 +194,7 @@
         data = b"hello world\nI'm not dead yet!\n"
         c.push_with_producer(data+SERVER_QUIT)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents, [b"hello world", b"I'm not dead yet!"])
 
@@ -206,7 +205,7 @@
         c.push(b"hello world\n\nI'm not dead yet!\n")
         c.push(SERVER_QUIT)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents,
                          [b"hello world", b"", b"I'm not dead yet!"])
@@ -225,7 +224,7 @@
         # where the server echoes all of its data before we can check that it
         # got any down below.
         s.start_resend_event.set()
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
 
         self.assertEqual(c.contents, [])
         # the server might have been able to send a byte or two back, but this
@@ -246,7 +245,7 @@
         self.assertRaises(TypeError, c.push, 'unicode')
         c.push(SERVER_QUIT)
         asyncore.loop(use_poll=self.usepoll, count=300, timeout=.01)
-        support.join_thread(s, timeout=TIMEOUT)
+        support.join_thread(s)
         self.assertEqual(c.contents, [b'bytes', b'bytes', b'bytes'])