Do not configure the root logger.

Calling `basicConfig` leaks to other custom defined loggers, so this leads to undesirable behavior. For example in this code example log messages gets printed out twice:

    logger = logging.getLogger('mylogger')
    logger.addHandler(logging.StreamHandler(sys.stdout))
    logger.setLevel(logging.INFO)

    loop = ioloop.IOLoop.current()
    loop._stopped = True
    loop.start()
    logger.info('Test')

This PR changes the check of handlers by adding only the basicConfig handlers to the Tornado loggers.