Wait "launch_second_activity" button to be gone

When running on slow devices (e.g. cuttlefish), the animation may take some time to start. The previous checks would pass if the animation didn't start and this causes an exception on the flicker tests

Test: atest FlickerTests
Change-Id: I8de4410e1c169d90d69d9a440daa82ec005fe222
1 file changed