Add tests for periodic jobs.

It's currently not feasible to test repeated runs of a periodic job, but
we can still test that they run in the appropriate windows and are
rescheduled after they run.

Bug: 30562670
Test: atest CtsJobSchedulerTestCases:TimingConstraintsTest
Change-Id: I14ad899e2926467920285fb6a66b7cfb193e917f
2 files changed