bpo-40275: Move transient_internet from test.support to socket_helper (GH-19711)

diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index ce60156..d1e3550 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -10,7 +10,7 @@
 import threading
 import socket
 
-from test.support import (reap_threads, verbose, transient_internet,
+from test.support import (reap_threads, verbose,
                           run_with_tz, run_with_locale, cpython_only)
 from test.support import hashlib_helper
 import unittest
@@ -968,16 +968,16 @@
     imap_class = imaplib.IMAP4
 
     def setUp(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             self.server = self.imap_class(self.host, self.port)
 
     def tearDown(self):
         if self.server is not None:
-            with transient_internet(self.host):
+            with socket_helper.transient_internet(self.host):
                 self.server.logout()
 
     def test_logincapa(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             for cap in self.server.capabilities:
                 self.assertIsInstance(cap, str)
             self.assertIn('LOGINDISABLED', self.server.capabilities)
@@ -986,7 +986,7 @@
             self.assertEqual(rs[0], 'OK')
 
     def test_logout(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             rs = self.server.logout()
             self.server = None
             self.assertEqual(rs[0], 'BYE', rs)
@@ -999,7 +999,7 @@
 
     def setUp(self):
         super().setUp()
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             rs = self.server.starttls()
             self.assertEqual(rs[0], 'OK')
 
@@ -1039,24 +1039,24 @@
             server.logout()
 
     def test_logincapa(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             _server = self.imap_class(self.host, self.port)
             self.check_logincapa(_server)
 
     def test_logout(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             _server = self.imap_class(self.host, self.port)
             rs = _server.logout()
             self.assertEqual(rs[0], 'BYE', rs)
 
     def test_ssl_context_certfile_exclusive(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             self.assertRaises(
                 ValueError, self.imap_class, self.host, self.port,
                 certfile=CERTFILE, ssl_context=self.create_ssl_context())
 
     def test_ssl_context_keyfile_exclusive(self):
-        with transient_internet(self.host):
+        with socket_helper.transient_internet(self.host):
             self.assertRaises(
                 ValueError, self.imap_class, self.host, self.port,
                 keyfile=CERTFILE, ssl_context=self.create_ssl_context())