Run face auth when bouncer is about to show

There may be a delay in showing the bouncer UI (~500ms)
to give face auth the opportunity to succeed
before showing the full bouncer UI. This CL makes sure
face auth begins before that 500ms delay, not after.

Fixes: 388363324
Flag: EXEMPT bugfix
Test: atest SystemUIDeviceEntryFaceAuthInteractorTest
Change-Id: Icf5c97aa8cadd76e26ea25046222b2aa483d072f