Validate a model's performance on a set of holdout data.

def main(argv):
    """Validate a model's performance on a set of holdout data."""
    _, *validation_paths = argv
    if FLAGS.expand_validation_dirs:
        tf_records = []
        with utils.logged_timer("Building lists of holdout files"):
            for record_dir in validation_paths:
                tf_records.extend(gfile.Glob(os.path.join(record_dir, '*.zz')))
    else:
        tf_records = validation_paths

    if not tf_records:
        raise RuntimeError("Did not find any holdout files for validating!")
    validate(*tf_records)