Merge changes from topic "migrate_CtsStagedInstallTest_RollbackTest"

* changes:
  Add multi-user test for the general non-staged case
  Increase timeout in testNativeWatchdogTriggersRollback
  Fix flaky testEnableRollbackTimeoutFailsRollback test
  Wait for available rollbacks in RollbackTest.
  Include NewRollbacks in result of getAvailableRollbacks.
  Rename RollbackData to Rollback.
  Remove INSTALLED_USERS extra from ACTION_PACKAGE_ENABLE_ROLLBACK.
  Update to new RollbackUtils.sendCrashBroadcast API.
  Extend ROLLBACK_COMMITTED broadcast for the multi-user case
  Fix NullPointerException.
  Cleanup some obsolete TODOs and unused code.
  Test Native Watchdog triggers RollbackManager rollback
  Uninstall testapps before running SecondaryUserRollbackTest
  delete ENABLING rollback if we can't get session info for it.
  Add test for rollback of userdata with multiple rollbacks
  Load rollback data in RollbackManagerServiceImpl constructor.
  Use "commit" for rollbacks instead of "execute".
  Add TestApi to block the RollbackManagerHandlerThread.
  Use Slog in RollbackManager, not Log
  Make setRequestDowngrade @TestApi
  Migrate RollbackTest and StagedRollbackTest to cts utils
  Add .apex suffix to apex files during validation
  Add host side test for secondary user rollback
  Reduce ENABLE_ROLLBACK timeout to 0 for timeout test.