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
Merge "Removes use of timeutils.set_time_override"