Fixing accessibility CTS tests.

1. Events from the popping IME were interfering with the ones from
   the starting activity.

2. Older events could lead to false positives in the execute and
   wait for event method.

3. Delegating service does not need a delay for receiving events.

bug:8487047

Change-Id: I38694dfc0d82001418bde629d678ef1f5f93c3c2