Tag Catalog Support For Metadata Definitions

[Wayne]

A challenge with using OpenStack is discovering, sharing, and correlating
tags across services and different types of resources. We believe this
affects both end users and administrators.

A catalog of possible tags that can be used to help ensure tag name consistency
across users, resource types, and services. So, when a user goes to apply a tag
on a resource, they will be able to either create new tags or choose from tags
that have been used elsewhere in the system on different types of resources.

The following DB schema is the initial suggested schema. We will improve and
take comments during code review. Constraints not shown for readability.
CREATE TABLE `metadef_tags` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `namespace_id` int(11) NOT NULL,
    `name` varchar(80) NOT NULL,
    `created_at` timestamp NOT NULL,
    `updated_at` timestamp
)

CREATE TABLE `metadef_tag_parents` (
    `child_tag_id` int(11) NOT NULL,
    `parent_tag_id` int(11) NOT NULL
)