Add shell commands to set flex policy.

Add shell commands to allow tests and developers to enable, disable, and
reset flex policy for testing and local development.

Bug: 244734471
Test: atest CtsJobSchedulerTestCases:FlexibilityConstraintTest
Change-Id: Id79d9b9ce93e4699d68ee76c1d1d7eba0b2c8815
3 files changed