bpo-40964: disable remote IMAP tests (GH-20836)

Remote host cyrus.andrew.cmu.edu is blocking incoming connections and is
causing test suite to fail.

Signed-off-by: Christian Heimes <christian@python.org>
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index f93efba..b8ab677 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -975,6 +975,7 @@
 
 @unittest.skipUnless(
     support.is_resource_enabled('network'), 'network resource disabled')
+@unittest.skip('cyrus.andrew.cmu.edu blocks connections')
 class RemoteIMAPTest(unittest.TestCase):
     host = 'cyrus.andrew.cmu.edu'
     port = 143
@@ -1010,6 +1011,7 @@
 @unittest.skipUnless(ssl, "SSL not available")
 @unittest.skipUnless(
     support.is_resource_enabled('network'), 'network resource disabled')
+@unittest.skip('cyrus.andrew.cmu.edu blocks connections')
 class RemoteIMAP_STARTTLSTest(RemoteIMAPTest):
 
     def setUp(self):
@@ -1025,6 +1027,7 @@
 
 
 @unittest.skipUnless(ssl, "SSL not available")
+@unittest.skip('cyrus.andrew.cmu.edu blocks connections')
 class RemoteIMAP_SSLTest(RemoteIMAPTest):
     port = 993
     imap_class = IMAP4_SSL