Following OpenStack Style Guidelines[1]:
[H203] Unit test assertions tend to give better messages for more
specific assertions. As a result, assertIsNone(...) is preferred
over assertEqual(None, ...) and assertIs(None, ...)
[1] http://docs.openstack.org/developer/hacking/#unit-tests-and-assertraises
Change-Id: Ie8136f1be4a57272e64b0b360ee608aa270901f7