Support find sensor screen with no animation

Some illustration view can manage their own start-stop lifecycle and
doesn't need to be handled by the activity.

Make mAnimation null if the animation is not an instance of
FingerprintFindSensorAnimation.

Test: cd tests/robotests && mma
Bug: 38463695
Change-Id: I41989e5cb0639407f58d9c8edda0eef93adbf2e8