cts: more test cases for transition animation selection

Construct a better test case to simulate failures due to
resuming before activityStopped() as in b/30255354. Stalling
onStop of the bottom activity by a certain amount, and let the
top activity finish before that ends. Use a second window to
allow the bottom activity to start animation even without
the main window (wallpaper target) relayout.

bug: 30255354

Change-Id: I8a6e9a9ca736165a439ab3a3b61c3226e8c8964a
4 files changed