Base Glance Metadata Definitions Admin UI

Provide a base admin UI for viewing, importing, and associating the
metadata definitions that can be used with various resource types
such as flavors, images, and host aggregates.

In Juno, Glance provided a metadata definitions catalog[1][2] where
users can register the available metadata definitions that can be used
on different types of resources (images, artifacts, volumes, flavors,
aggregates, etc). This includes key / value pairs such as
properties, extra specs, etc. Horizon landed several patches that
read these properties. You can view the functionality in the
"update metadata" action on Flavors, Images, and Host Aggregates.

This specific patch is to bring in the Admin UI for the basic coarse
grained actions on the definitions in the catalog. This includes creating
(importing) a namespace, viewing the overview details about
it, deleting the namespace, and associating the namespace for use with
specific resource types.

Future blueprints will be registered for:
 - CRUD on individual metadata definitions within the namespace
For example, editing the default value of an individual property.

[1] Approved Glance Juno Spec:
https://github.com/openstack/glance-specs/blob/master/specs/juno/metadata-schema-catalog.rst

[2] Glance PTL Juno Feature Overview:
https://www.youtube.com/watch?v=3ptriiw1wK8&t=14m27s

Co-Authored-By: Travis Tripp <travis.tripp@hp.com>
Co-Authored-By: Santiago Baldassin<santiago.b.baldassin@intel.com>
Co-Authored-By: Bartosz Fic <bartosz.fic@intel.com>
Co-Authored-By: Pawel Koniszewski <pawel.koniszewski@intel.com>
Co-Authored-By: Michal Dulko <michal.dulko@intel.com>
DocImpact: Concept awareness
Change-Id: Ie34007f73af7e0941631a52f03841068e509a72c
Implements: blueprint glance-metadata-definitions-base-admin-ui
Merge "Base Glance Metadata Definitions Admin UI"