Fix non-deterministic async test

See comments in TimeZoneDetectorCallbackImpl for details.
This is to fix testManageConfiguration.

Bug: 171221358
Bug: 171953500
Test: Ran atest TimeManagerTest with
  location_time_zone_detection_enabled set to 0 and 1
Change-Id: Ife146a5cc9c77a14c45167d70314d248d14445e1