Allow multiple emulated storages at the same time.

Only do multiuser mapping for primary emulated storage as per google docs.
Allow all non-primary emulated storage to have id other than 0 so that
it could be distinguished from the primary volume.

Change-Id: I7b70b9067fd6211055fb9074710f48107d7b0e8e
KeyguardViewMediator: Play lock screen sound sooner

When the screen is locked, there is a long pause before the lock
sound actually plays.

This makes that sound happen much sooner.

Change-Id: Iede7a5d22291d1ada98800d2b380c255547df61d