[BZ 1161806] Switch the entire server metrics code to use an UTC timezone in all the code. This will avoid any DST issues since there is no DST in UTC timezone. Also, this will avoid any problems due to having an HA environment where the servers are distributed in different timezones.
[BZ 1161806] Shift the timeslice to a correct UTC timeslice during the index migration. This will gurantee that during metrics index updates the new indexes have slices based on UTC timezone.
[BZ 1161806] Fix broken unit tests due to timeslice shift to UTC timezone based.
[BZ 1161806] Update the migration code to handle cases where the data spans a DST change. Without this change, the code will not be able to properly retreive indexes that if the start date is before the DST transition and end date is after the DST transition.