Reduce flakiness of WmTests

1. Same as I1b2eb77585ba0a1ee936ee921af95e9c2113ec63
   that waits for the completion of Activity#onDestroy.
2. Relax assertion of surfaceChanged count that occasionally
   an additional change may appear if the app updates earlier.

Fix: 293499710
Fix: 294403114
Test: atest TrustedPresentationCallbackTest SurfaceControlTests
Change-Id: I67daae8d17bc647af1d188d229dcfb064911f3b0