DO NOT MERGE. Update lockscreen message when user unlocked.

If a user doesn't have credentials, we start the unlock process
automatically, but that races with the UI binding process.  Fix by
rebinding the UI once we hear the user is unlocked.

Change-Id: Id678b97aa6120ba78088fb6cf4c2a65d129e98a3
Test: none
Bug: 30840626
(cherry picked from commit 18100137)