[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>
[SPARK-4107] Fix incorrect handling of read() and skip() return values (branch-1.1 backport)

`read()` may return fewer bytes than requested; when this occurred, the old code would silently return less data than requested, which might cause stream corruption errors.  `skip()` faces similar issues, too.

This patch fixes several cases where we mis-handle these methods' return values.

This is a backport of #2969 to `branch-1.1`.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #2974 from JoshRosen/spark-4107-branch-1.1-backport and squashes the following commits:

d82c05b [Josh Rosen] [SPARK-4107] Fix incorrect handling of read() and skip() return values
[SPARK-4065] Add check for IPython on Windows

This issue employs logic similar to the bash launcher (pyspark) to check
if IPTYHON=1, and if so launch ipython with options in IPYTHON_OPTS.
This fix assumes that ipython is available in the system Path, and can
be invoked with a plain "ipython" command.

Author: Michael Griffiths <msjgriffiths@gmail.com>

Closes #2910 from msjgriffiths/pyspark-windows and squashes the following commits:

ef34678 [Michael Griffiths] Change build message to comply with [SPARK-3775]
361e3d8 [Michael Griffiths] [SPARK-4065] Add check for IPython on Windows
9ce72d1 [Michael Griffiths] [SPARK-4065] Add check for IPython on Windows

(cherry picked from commit 2f254dacf4b7ab9c59c7cef59fd364ca682162ae)
Signed-off-by: Andrew Or <andrew@databricks.com>