services: Workaround for our face unlock initialization [1/2]

AuthService registers the authenticators only once and
then onAllAuthenticatorsRegistered() callbacks are invoked.
The callbacks are removed as soon as it invoked.

Our LMO face unlock authenticator isn't being registered via AuthService.
When we register it, the onAllAuthenticatorsRegistered() callbacks aren't available
at that time so our face unlock isn't being initialized properly
and end up with bugs like "Face unlock isn't working after reboot".

As a workaround, we don't invoke callbacks if it's first time (from AuthService).
Instead we register our face unlock here on first time to make sure
callbacks are being called only after our face unlock authenticator registration.

If properties aren't empty, it's from hardware face sensor.
so allow to invoke callbacks regardless of the first time.

Change-Id: I26238a35f09d9cb398355d9467d44cd24b0e2525