auth_token tests use assertIs/Not/None

The tests in test_auth_token_middleware were using
assertEqual(res, None) and assertNotEqual(res, None) when they
should use assertIsNone and assertIsNotNone.

Change-Id: Ib1601b3a6101f843d9c29f3cd00aab339e671e61
Merge "auth_token tests use assertIs/Not/None"