Use real gatekeeper HAT for resetting lockout

The code is slightly confusing in that synthetic password response also
contains a gatekeeper response. This is not the actual response that
contains the challenge. Instead, we should be using the second response
from gateeper, which is the real gatekeeper auth token.

Fixes: 133444358

Test: Before change, get locked out, enter password, user stays locked out
      After change, get locked out, enter password, lockout is reset

Change-Id: Ia869fe5d1ebdb91263b3494da2fba5f3c6304047