Fix Keyboard flicker

Bouncer should not be focusable if we are on Keyguard and not
occluded, and we don't need the IME. Otherwise, we'd see a flicker
of the IME animating out when the bouncer comes up on pattern/PIN
screens.

Test: Set pattern, open app with IME open, lock screen, dismiss
Keyguard.
Test: Set password, dismiss Keyguard.

Bug: 32894573
Change-Id: I25da76b66b1cd5722d5929bb2d2658282faef517