Change context assignment mechanism.

Attempt to assign to empty contexts before trying to stop running jobs.

Bug: 141645789
Bug: 223437753
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: Id6b0602547e13abd3d23a869a14857f07606a274
3 files changed