'Return the value for a specific image metadata key.'

def show_image_metadata_item(self, image_id, key):

    (resp, body) = self.get(('images/%s/metadata/%s' % (image_id, key)))
    body = json.loads(body)
    self.validate_response(schema.image_meta_item, resp, body)
    return rest_client.ResponseBody(resp, body)
