update trust state immediately when user auths via FP on keyguard

KeyguardUpdateMonitor onFingerprintAuthenticated currently doesn't
immediately update the trust state. TrustManager.isDeviceLocked()
should return "unlocked" after FP is authenticated.

Fixes: 37963501

Test: Two tests as follows

1) use custom app that polls isDeviceLocked(), make sure
it returns "unlocked" after FP is authenticated but keyguard is showing.
To get that state, slide keyguard up slightly and touch FP sensor
without letting go of the other finger.

2) with at least 2 accounts, run the app on both accounts.
when switching users, the app should show that the "inactive/underneath"
user is locked. the app should report that the current user is locked
before touching fp, and unlocked after touching fp

Change-Id: I2a11411deebf369d85dee62cffdcd631bd99649f