Don't attempt dismiss while user switch is in progress

This may rely on values from the prior user, resulting in the
incorrect bouncer being shown. Wait until the user switch
is complete before attempting to dismiss keyguard, or show
bouncer.

Fixes: 368017647
Test: atest KeyguardViewMediatorTest
Flag: EXEMPT bugfix
Change-Id: Ic8c2cc62ac0528762245b212ed0bf63969c86668