Call with Shell transition for TRANSIT_KEYGUARD_OCCLUDE/UNOCCLUDE

Before, it only called with legacy app transition, so it sometimes
missed to collect for occlude change.

Also remove some duplicated prepareAppTransition call.

Bug: 193564917
Test: passed KeyguardTests with Shell transition is on
Change-Id: Ie5a445466f2a71fd6125af09e311ee754611e5ae