[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`.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2972 from sarutak/SPARK-4110 and squashes the following commits:

5a171a2 [Kousuke Saruta] Fixed wrong comments

sbin/spark-daemon.sh

@@ -21,8 +21,8 @@
 #
 # Environment Variables
 #
-#   SPARK_CONF_DIR  Alternate conf dir. Default is ${SPARK_PREFIX}/conf.
-#   SPARK_LOG_DIR   Where log files are stored.  PWD by default.
+#   SPARK_CONF_DIR  Alternate conf dir. Default is ${SPARK_HOME}/conf.
+#   SPARK_LOG_DIR   Where log files are stored. ${SPARK_HOME}/logs by default.
 #   SPARK_MASTER    host:path where spark code should be rsync'd from
 #   SPARK_PID_DIR   The pid files are stored. /tmp by default.
 #   SPARK_IDENT_STRING   A string representing this instance of spark. $USER by default