Deferring low and min priority jobs when quota is low.

Make sure there is some minimum amount of quota available for higher
priority jobs before we start running lower priority jobs.

Bug: 205714315
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/job
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Test: atest CtsJobSchedulerTestCases
Change-Id: I87919e08684fe1012bfc66d7fae928d04f575637