Don't show Face Unlock on initial boot fixes 6396685

Uses a static to keep track whether this is the first pass through the lockscreen
This will be true from when the process is instantiated until the lockscreen
is constructed for the first time, and then false afterwards.
When it is true, we suppress the biometric unlock (Face Unlock).
This avoids the problem of unpredictable and slow startup behavior for Face Unlock
on the first unlock after boot.

Change-Id: I70033af17ba3163d5fe07fc58096f01afaaaafd0