Removes use of timeutils.set_time_override

The set_time_override function in timeutils was written as a
helper function to mock utcnow for unittests before 'mock' was
generally used. Now that we have mock and fixture, we no longer
need to use it.

Partial-Bug: #1266962

Change-Id: I56935911a08ccd9847419eb118af2d2c9dd6c1cd
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 "Removes use of timeutils.set_time_override"
Merge "auth_token tests use assertIs/Not/None"