Comment 3 for bug 1520625

This is being discussed in upstream. Please see the following bugreports and reviews.

https://review.openstack.org/#/c/249863/
https://review.openstack.org/#/c/231191/
https://launchpad.net/bugs/1473567
https://launchpad.net/bugs/1517697
https://review.openstack.org/#/c/243742/

TL;DR: this is a race condition in keystone/tempest related to revocation events and can be fixed in both keystone or tempest. We can either wait for it to get fixed in upstream or apply patches to our tempest now.