Wait for enter animation to complete when calling startActivitySync

Tests may need to wait until the Activity's enter animation
is complete before executing. This is to make sure the windows
are all in the correct place. This change ensures the startActivitySync
waits on enter animation to complete for that activity before
proceeding.

Change-Id: Ifd7bfd41b39518518f4013fad80c3acd1e8b2354
Fixes: 120430810
Test: InstrumentationTest#testSendPointerSync