In Juno, this parameter is required otherwise Glance can't
authentificate against Keystone.
There is a patch in puppet-glance:
https://review.openstack.org/#/c/133521/ but not merged yet (still under
discussion). In the meantime, let's fix it in the composition layer.
Change-Id: I8ab9ab365ad5c9266c9e71054d8b43ecbaef50ac