Fixing issue with swipe-dismiss animation clobbering home animation.

- Finish all dismiss animations when a dismiss-to-home animation is 
  started, and prevent lingering deferred layout animation requests
  from running as they will be overwritten anyways.

Bug: 28287904
Change-Id: Ie40c66c0f25705b56f6808607d2b7b8ae4e5a112