[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

(cherry picked from commit 44d8b45a38c8d934628373a3b21084432516ee00)
Signed-off-by: Andrew Or <andrew@databricks.com>