RESTRICT AUTOMERGE

Prevent non-system overlays from showing over CDM UI

Since CDM grants privileges, it should have the same overlay
policy as permission UI

Test: use an app wit ha visible overlay to ensure
the overlay disappears when CDM is shown
Fixes: 171221090

Change-Id: I4daaee7d8b710a72f6166cbb2252ef8af84c2c60