Fix 5451144: Poking wakelock upon fallback

Now poking the wakelock when Face Unlock goes to the fallback method.
Previously, the backup lock would stay up for a varying amount of
time depending on how long Face Unlock took before fallback.  The
backup is now consistently displayed for 5 seconds.

Also added comments to some older code.

Change-Id: I9f6bdd2d3015e7eb9cb90143737a3cdc87189993