Keyguard should wait before restarting FP auth after successful FP auth

There exists a race condition where Keyguard restarts authentication
after onResume of the application underneath (which may also use FP auth).

This also fixes an issue where a user can receive a second successful
authentication if they tap quickly after the first authentication while
keyguard is going away.

Fixes: 63896908

Test: manual test of the above two scenarios
Change-Id: I0a27939cb85fc4ccad4aabfab36a2a8ffe38ac9c