'Delete an image tag.
For a full list of available parameters, please refer to the official
API reference:
http://developer.openstack.org/api-ref/image/v2/#delete-image-tag'

def delete_image_tag(self, image_id, tag):

    url = ('images/%s/tags/%s' % (image_id, tag))
    (resp, _) = self.delete(url)
    self.expected_success(204, resp.status)
    return rest_client.ResponseBody(resp)
