User switching on boot race condition - unit tests

Add some tests that check if a user switch is in progress
on startup, and if so, will manually invoke onUserSwitching()

Fixes: 365707550
Test: atest KeyguardUpdateMonitorTest KeyguardViewMediatorTest
Flag: EXEMPT bugfix
Change-Id: If1b569dde3f8efd9dbb14bfe5693ce9d6e82daa3