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: I8964a10ae3529e978bfab1d8140f95da4b56615c

Author: EinstCrazy

openstackclient/tests/identity/v3/test_service_provider.py

@@ -408,5 +408,5 @@ def prepare(self):
         # expect take_action() to return (None, None) as none of --disabled,
         # --enabled, --description, --service-provider-url, --auth_url option
         # was set.
-        self.assertEqual(columns, None)
-        self.assertEqual(data, None)
+        self.assertIsNone(columns)
+        self.assertIsNone(data)