Keystore needs to be able to call apps

The ConfirmationUI API has a callback interface by which confirmation
results are presented to the calling app. This requires keystore to call
into apps.

Test: Device boots and no more denials when call back is delivered to
      apps.
Bug: 63928580
Change-Id: Ie23211aeb74c39956c3c3b8b32843d35afa1315a