Unbinding from FU when going to backup

Lockscreen was stopping Face Unlock when going to the backup lock, but
not unbinding from the Face Unlock service until the device was
unlocked.

This caused a bug on the tablets where Face Unlock would reappear when
switching between portait and landscape orientations, even after the
backup lock was exposed.  On an orientation change, Face Unlock is
restarted if the service is bound to during the orientation change.
Since it was bound to when it should not have been, Face Unlock was
restarting when it should not have been.

The wakelock is also now being poked on an orientation change because
on the tablet you can keep Face Unlock alive by switching the
orientation back and forth, but eventually the screen would go dark
with Face Unlock running.

Also, a conditional was moved in activateFaceLockIfAble() so the whole
section isn't executed if Face Unlock is not in use.  Part of it was
being executed with only the inner-most part having the check.  This
did not cause any issues that I am aware of.

Change-Id: Ib452b8ced28a507bf9272dbf5d3477a8abd1ba90