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: I004843edf5a156dc07fb961edf80272f5cb50163
(cherry picked from commit ea4ce4d4)
Merged-In: I004843edf5a156dc07fb961edf80272f5cb50163