Reslove print has not flush output to file

    解决print没有实时写入日志文件问题
    More info, please refer to:
    http://stackoverflow.com/questions/107705/python-output-buffering
    1.Use the -u command line switch
    2.Wrap sys.stdout in an object that flushes after every write
    3.Set PYTHONUNBUFFERED env var
    4.sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
    also,see http://fosschef.com/2011/02/python-stdout-and-buffering/