Setup default logger

def _default(cls, opts):
        """Setup default logger"""
        level = getattr(logging, opts.log_level, logging.DEBUG)

        logger = logging.getLogger('luigi-interface')
        logger.setLevel(level)

        stream_handler = logging.StreamHandler()
        stream_handler.setLevel(level)

        formatter = logging.Formatter('%(levelname)s: %(message)s')
        stream_handler.setFormatter(formatter)

        logger.addHandler(stream_handler)
        return True