This informs operators of glance's support status for secure RBAC as of
the Wallaby release. Eventually, this message will be removed when
glance adopts more support for secure RBAC personas.
This also forces glance to fail if it's configured improperly. This is
done to explicitly prevent ambiguity with authoritative decisions.
Related: blueprint secure-rbac
Change-Id: I06293de08dd3fdfbd60b9a65501d1198f40ff434