Add tests for private profile delayed locking

This change adds UserControllerTests for testing the delayed locking
flows for private profile. The following scenarios are covered:
- Private profile should be stopped and locked if stopUser is called
- Private profile should be stopped and locked if
  stopUserWithDelayedLocking is called but the private profile feature
  flags are disabled
- Private profile should be stopped and locked if
  stopUserWithDelayedLocking is called but mMaxRunningUsers is less than
  the total running users
- Private profile should be stopped and unlocked if
  stopUserWithDelayedLocking is called with private profile flags turned
  on and mMaxRunningUsers greater than the total running users

Test: atest UserControllerTests
Bug: 312184187

Change-Id: I2af727edf52340c9f4b64614715f70226b88fd75