[H203] Use assertIs(Not)None to check for None (off by default) Unit
test assertions tend to give better messages for more specific
assertions. As a result, assertIsNone(...) is preferred over
assertEqual(None, ...) and assertIs(None, ...), and assertIsNotNone(...)
is preferred over assertNotEqual(None, ...) and assertIsNot(None,
...). Off by default.
More details, see:
http://docs.openstack.org/developer/hacking/#unit-tests-and-assertraises
Trivial fix.
Change-Id: Icd268b96dea5e5bb9bd344f597dfcd9cc82253f0