Command: docker_image_ids

def docker_image_ids(broker):
        """Command: docker_image_ids"""
        images = broker[DefaultSpecs.docker_list_images]
        try:
            result = set()
            for l in images.content[1:]:
                result.add(l.split(None)[3].strip())
        except:
            raise ContentException("No docker images.")
        if result:
            return list(result)
        raise ContentException("No docker images.")