(PUP-3429) task_scheduler should use 'day_of_week' instead of 'on'

Populate 'day_of_week' instead of 'on' when loading existing triggers. This
should prevent constant changes from being registered.
Merge branch 'ticket/master/PUP-3429-weekly-task_scheduler'

* ticket/master/PUP-3429-weekly-task_scheduler:
  (PUP-3429) task_scheduler should use 'day_of_week' instead of 'on'