Clean up all dangling images.

def clean_up_dangling_images(self):
        """
        Clean up all dangling images.
        """
        cargoes = Image.all(client=self._client_session, filters={'dangling': True})
        for id, cargo in six.iteritems(cargoes):
            logger.info("Removing dangling image: {0}".format(id))
            cargo.delete()