Execute app transition when start locking task

This issue always existed but now only became visible because
occluding/unoccluding Keyguard relies on activity transitions.

Test: Have pattern, lock task, unlock without 5 seconds, make sure
activity is not lingering around.
Bug: 32771855

Change-Id: Ib75bf904dd69db64bd64d13d518897ce9cf44394
1 file changed