Ignoring FUL unlock signal if user changed fixes b/7572354

Prior to this fix, one user could log into another user's account by
waiting for FUL to recognize them on their account, and then
switching to another account at a very precise time - after FUL has
recognized the user but before the device has unlocked.

This was caused by the FUL unlock() callback telling the device to
unlock even though the user had changed.  The fix is to only unlock
the device if the current user ID matches the user ID used to run
FUL.

Change-Id: I516b52d99ab7609b836939e4aae6e7df77a9e047