Bind fingerprint when we start authentication

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

(Cherry pick from Change-Id: I346d92c301414ed81e11fa9c171584c7ae4341c2)

Change-Id: I3584790c39eb2e8c435ad1b2d887bf9b8ebd36fe
(cherry picked from commit 837d052ed4b5b75dfd4af44f5ad268e683bf2e13)
