Fix 5437700: Underlying backup method was exposed

At one point we added a timeout to the black box that covers the
underlying backup unlock method so if Face Unlock doesn't start or
crashes, the user will see the backup method rather than being stuck
looking at a black box.  However, when powering the phone on and off
quickly, the message to time out the black box could be received at
the wrong time, causing it to expose the underlying backup method
when it shouldn't.

This solution clears the existing SHOW/HIDE messages from the
handler's message queue before sending a new SHOW/HIDE message.  In
particular, it clears out a delayed HIDE message when a SHOW is sent
so the SHOW can't be undone by a pending delayed HIDE message.

Also, logging errors for a couple of exceptions instead of rethrowing
so we can gracefully go to the backup in these cases.

Patch set 2 fixes problem where rare exceptions could prevent ever
binding to the service again because mBoundToFaceLockService was still
true.

Change-Id: Ieb7b6723161070f509277f67dc9ef100cf7c1aa6