'Delete image metadata item for the volume.'

def delete_volume_image_metadata(self, volume_id, key_name):

    post_body = json.dumps({'os-unset_image_metadata': {'key': key_name}})
    url = ('volumes/%s/action' % volume_id)
    (resp, body) = self.post(url, post_body)
    self.expected_success(200, resp.status)
    return rest_client.ResponseBody(resp, body)
