Replace assertEqual(None, *) with assertIsNone in tests

Replace assertEqual(None, *) with assertIsNone in tests to have
more clear messages in case of failure.

Change-Id: I0578063d719293d5f2e838241c2db96454f7e4b6
Closes-bug: #1280522
diff --git a/tempest/tests/test_glance_http.py b/tempest/tests/test_glance_http.py
index ed886da..db9db34 100644
--- a/tempest/tests/test_glance_http.py
+++ b/tempest/tests/test_glance_http.py
@@ -123,9 +123,9 @@
     def test_get_connection_kwargs_default_for_https(self):
         kwargs = self.client._get_connection_kwargs('https')
         self.assertEqual(600, kwargs['timeout'])
-        self.assertEqual(None, kwargs['ca_certs'])
-        self.assertEqual(None, kwargs['cert_file'])
-        self.assertEqual(None, kwargs['key_file'])
+        self.assertIsNone(kwargs['ca_certs'])
+        self.assertIsNone(kwargs['cert_file'])
+        self.assertIsNone(kwargs['key_file'])
         self.assertEqual(False, kwargs['insecure'])
         self.assertEqual(True, kwargs['ssl_compression'])
         self.assertEqual(6, len(kwargs.keys()))