Rework expedited status.

Change the OK for a job to be treated as expedited from a "constraint"
to a boolean. This will make it a little nicer to add different ways of
approving a job to be treated as expedited.

Bug: 158300259
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/job
Test: atest CtsJobSchedulerTestCases
Change-Id: Id1c85b0bbdd7201ab325b0ef71f764c578869fd7