[SPARK-4110] Wrong comments about default settings in spark-daemon.sh

In spark-daemon.sh, thare are following comments.


    #   SPARK_CONF_DIR  Alternate conf dir. Default is ${SPARK_PREFIX}/conf.
    #   SPARK_LOG_DIR   Where log files are stored.  PWD by default.

But, I think the default value for SPARK_CONF_DIR is `${SPARK_HOME}/conf` and for SPARK_LOG_DIR is `${SPARK_HOME}/logs`.