UserAwareBiometricScheduler lifecycle fix.

Fixed an issue where UserAwareBiometricScheduler queue would get stuck
indefinitely(causing face/fingerprint to fail until reboot).

Testing steps to reproduce

Setup.
* Have multiple users with multipler biometrics.

1. Add a property in a biometric HAL(Call it biometric A) to hang on auth operation
2. Set property to hang when authenticating(biometric A).
3. Unlock device with alternative biometric(biometric B)/pin/pattern/pass
4. Unset property to stop biometric(biometric A) from hanging
5. Rinse and repeat 1-4 until a hang occurs

Test: Manual (See above)
Test: atest UserAwareBiometricSchedulerTest
Fixes: 234625004
Change-Id: Ia6055ef3314ddaf986d5dfb4b642a5aba183053d