Glance Metadata Definitions Catalog - API

Implements: blueprint metadata-schema-catalog

A common API hosted by the Glance service for vendors, admins,
services, and users to meaningfully define available key / value
pair and tag metadata. The intent is to enable better metadata
collaboration across artifacts, services, and projects for
OpenStack users.

This is about the definition of the available metadata that can
be used on different types of resources (images, artifacts,
volumes, flavors, aggregates, etc). A definition includes the
properties type, its key, it's description, and it's constraints.
This catalogue will not store the values for specific instance
properties.

 - REST API for CRUD on metadef namespace
 - REST API for CRUD on metadef objects
 - REST API for CRUD on metadef properites
 - REST API for CRUD on metadef resource types
 - REST API for JSON schemas on metadef API's

Change-Id: I8e6d88ffee9a9337bf82b1da85648ba638a154ab
DocImpact
Co-Authored-By: Lakshmi N Sampath <lakshmi.sampath@hp.com>
Co-Authored-By: Wayne Okuma <wayne.okuma@hp.com>
Co-Authored-By: Travis Tripp <travis.tripp@hp.com>
Co-Authored-By: Pawel Koniszewski <pawel.koniszewski@intel.com>
Co-Authored-By: Michal Jastrzebski <michal.jastrzebski@intel.com>
Co-Authored-By: Michal Dulko <michal.dulko@intel.com>