Add exemptions to flex policy.

Exempt DEFAULT+ priority jobs for BFGS+ and exempted apps from flex
policy. LOW and MIN priority jobs will continue to have the flex policy
applied.

Also make the run shell command more reliable for connectivity jobs.

Bug: 236261941
Bug: 299329948
Bug: 299346198
Bug: 316435418
Test: atest CtsJobSchedulerTestCases:FlexibilityConstraintTest
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Test: atest
frameworks/base/services/tests/servicestests/src/com/android/server/job

Change-Id: Ic774f541b8bf64aecc814eba991008ebaeba3566