Add usermanager related perf tests - part2

- Add onLockedBootComplete callback to UserSwitchObserver.

Bug: 30948225
Test: adb shell am instrument -e class android.multiuser.UserLifecycleTest -w com.android.perftests.multiuser/android.support.test.runner.AndroidJUnitRunner
Change-Id: I87533094805a81fbd85d4f492e637b3304ecd5e2