Endpoint id is not predictable so users can't configure the endpoint_id
option until keystone endpoints are created. This requires redundant
steps in deployment. For example both keystone and glance are run by
httpd + mod_wsgi then you first have to deploy keystone and then create
glance endpoints, until you can install glance and restart httpd.
This introduces a few new options to look up the target endpoint from
Keystone. All these options accept predictable values.
Closes-bug: #1931875
Change-Id: I0411d4aa6abd86cb38bf3c1999f2bae213983078
9575a24796