Use Keyguard orientation when unoccluding

If we are about to unocclude Keyguard, we already use its
orientation spec such that if both Keyguard and the activity
going aways share the same orientation spec, there is no
unnecessary orientation change.

Test: Launch SHOW_WHEN_LOCKED portrait activity, hold device
in landscape, toggle power button twice, press home, make sure
no orientation change when animating to Keyguard.
Test: go/wm-smoke

Change-Id: Ic5f110747de5f5f7d73adf83f5f53c7fd56d860c
Fixes: 38146081