Cancel authentication when secure camera is launched on Keyguard

To decrease potential latency in starting the secure camera, rather than
waiting for keyguard to become occluded and canceling authentication, we
pre-emptively cancel face auth on keyguard when double tap is activated.
This saves hundreds of ms.

Fixes: 134613755

Test: With added logging, observed that cancel is now invoked immediately
      when double tap for camera is triggered.

Change-Id: I3740c55fb608cd1f8aa228768389f192cf18d557