'Gets a definition for a tag.
For a full list of available parameters, please refer to the official
API reference:
https://developer.openstack.org/api-ref/image/v2/metadefs-index.html#get-tag-definition'

def show_namespace_tag(self, namespace, tag_name):

    url = ('metadefs/namespaces/%s/tags/%s' % (namespace, tag_name))
    (resp, body) = self.get(url)
    self.expected_success(200, resp.status)
    body = json.loads(body)
    return rest_client.ResponseBody(resp, body)
