Bug 1167565

This update adds a common API hosted by the Image Service (glance) for vendors, admins, services, and users to meaningfully define an available key/value pair, and tag metadata. The intent is to enable better metadata collaboration across artifacts, services, and projects for OpenStack users. This definition describes the available metadata that can be used on different types of resources (images, artifacts, volumes, flavors, aggregates, among others). A definition includes the properties type, key, description, and constraints. This catalog will not store the values for specific instance properties. For example, a definition of a virtual CPU topology property for a number of cores will include the key to use, a description, and value constraints, such as requiring it to be an integer. As a result, users (potentially through the dashboard) would be able to search this catalog to list the available properties they can add to a flavor or image. They will see the virtual CPU topology property in the list and know that it must be an integer. In the dashboard example, when the user adds the property, its key and value will be stored in the service that owns that resource (in nova for flavors, and in glance for images).