Cinder ignores reader role conventions in default policies

[Lance Bragstad]

In keystone, if I grant someone the reader role on a project [0], they're able to make writable changes in cinder.

Opening this bug to track work for cinder to consume keystone's default read-only `reader` role.

[0] $ openstack --os-cloud devstack-system-admin role add --user alice --user-domain default --project foobar --project-domain default reader

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Luigi Toscano <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/cinder-tempest-plugin/+/778357
Reason: The scope of protection/RBAC test changed a bit over time, and other changes addressed and will address the use case of this review in a slightly different way. See for example https://review.opendev.org/c/openstack/cinder-tempest-plugin/+/878672 and other related changes