WADL to RST migration (part 2 - metadefs)

This brings the Images API Reference to the glance tree as part of
the effort described here:
https://wiki.openstack.org/wiki/Documentation/Migrate#API_Reference_Plan

This patch includes the Metadefs API reference, with the content
revised and corrected.

Change-Id: I8c10893e92edb7c608b58d33539ab57ab4f57d3e
Closes-bug: #1599314

Author: bria4010

api-ref/source/index.rst

@@ -24,3 +24,4 @@ Image Service APIs
    versions/index
    v1/index
    v2/index
+   v2/metadefs-index

api-ref/source/v2/metadefs-index.rst

@@ -0,0 +1,62 @@
+..
+      Copyright 2010 OpenStack Foundation
+      All Rights Reserved.
+
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+:tocdepth: 3
+
+=============================================
+Metadata Definitions Service API v2 (CURRENT)
+=============================================
+
+.. rest_expand_all::
+
+Metadefs
+********
+
+General information
+~~~~~~~~~~~~~~~~~~~
+
+The Metadata Definitions Service ("metadefs", for short) provides a common API
+for vendors, operators, administrators, services, and users to meaningfully
+define available key:value pairs that can be used on different types of cloud
+resources (for example, images, artifacts, volumes, flavors, aggregates, etc).
+To get you started, Glance contains a default catalog of metadefs that may be
+installed at your site; see the `README
+<https://github.com/openstack/glance/tree/master/etc/metadefs/README>`_ in the
+code repository for details.
+
+Once a common catalog of metadata definitions has been created, the catalog is
+available for querying through the API.  Note that this service stores only the
+*catalog*, because metadefs are meta-metadata.  Metadefs provide information
+*about* resource metadata, but do not themselves serve as actual metadata.
+
+Actual key:value pairs are stored on the resources to which they apply using
+the metadata facilities provided by the appropriate API.  (For example, the
+Images API would be used to put specific key:value pairs on a virtual machine
+image.)
+
+A metadefs definition includes a property’s key, its description, its
+constraints, and the resource types to which it can be associated.  See
+`Metadata Definition Concepts
+<http://docs.openstack.org/developer/glance/metadefs-concepts.html>`_ in the
+Glance Developer documentation for more information.
+
+
+.. include:: metadefs-namespaces.inc
+.. include:: metadefs-resourcetypes.inc
+.. include:: metadefs-namespaces-objects.inc
+.. include:: metadefs-namespaces-properties.inc
+.. include:: metadefs-namespaces-tags.inc
+.. include:: metadefs-schemas.inc