Bind fingerprint when we start authentication - DO NOT MERGE

This fixes a bug where it was possible to authenticate the wrong user.
We now bind the userId when we start authentication and confirm it when
authentication completes.

Fixes bug 30744668

RM-290

Change-Id: I346d92c301414ed81e11fa9c171584c7ae4341c2
(cherry picked from commit b6f4b48d)