//the format of the index file is
      //LOG_DIR: <the dir where the task logs are really stored>
      //STDOUT: <start-offset in the stdout file> <length>
      //STDERR: <start-offset in the stderr file> <length>
      //SYSLOG: <start-offset in the syslog file> <length>
//the format of the index file is
      //LOG_DIR: <the dir where the task logs are really stored>
      //STDOUT: <start-offset in the stdout file> <length>
      //STDERR: <start-offset in the stderr file> <length>
      //SYSLOG: <start-offset in the syslog file> <length> | TaskLog.java