project disabled/deleted notification recommendations

These recommendations represent the outcome of the Keystone/Barbican
cross-project discussion regarding:

  https://review.openstack.org/#/c/99658/

This discussion occurred at the keystone hackathon for Juno.

Change-Id: Ib67c85a9f900ef0a6a346cdbf3280b3a8f977ad7
Merge "project disabled/deleted notification recommendations"