Make testing jobs easier.

1. Add a flag to only run a job if its constraints are satisfied.
2. Put jobs that have been requested to run via adb at the front of the
list so they hopefully run first.

Bug: 138253466
Test: atest CtsJobSchedulerTestCases
Change-Id: I8dac5ff9b39e02a051346c59a011f494842f4fc8