Ensuring KeyguardService has the correct user when it starts

Because RetailDemoModeService was switching user before KeyguardService
was started, KeyguardViewMediator was missing the call to setCurrentUser
on user switch. Setting the current user from keyguardState in
onServiceConnected, if there was a user switch that happened earlier.
Also changed RetailDemoModeService to switch user after it receives boot
phase BOOT_COMPLETE.

Bug: 30038980
Change-Id: I142570529097199ccc50849297ae67ca49d35534