bpo-38614: Use test.support.LONG_TIMEOUT constant (GH-17562)

Replace hardcoded timeout constants in tests with LONG_TIMEOUT of
test.support, so it's easier to ajdust this timeout for all tests at
once.

LONG_TIMEOUT is 5 minutes by default, but it can be longer depending
on --timeout command line option.
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 3b135b8..4feed03 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -1059,8 +1059,8 @@
 # - end of server_helper section
 
 class SMTPHandlerTest(BaseTest):
-    # bpo-14314, bpo-19665, bpo-34092: don't wait forever, timeout of 1 minute
-    TIMEOUT = 60.0
+    # bpo-14314, bpo-19665, bpo-34092: don't wait forever
+    TIMEOUT = support.LONG_TIMEOUT
 
     def test_basic(self):
         sockmap = {}