Setting c.get_auth_keystone = fake_get_auth_keystone is setting a new
method on the module. This information is not reset between test runs
and therefore has the potential to corrupt other tests.
Use mock patch so that the mock is reset after the test is complete.
Change-Id: Ifb9ba72634cf477c72dda080b5aed8f8e3a7ac89
fd675b2c5a