SPARK-3178  setting SPARK_WORKER_MEMORY to a value without a label (m or g) sets the worker memory limit to zero

Validate the memory is greater than zero when set from the SPARK_WORKER_MEMORY environment variable or command line without a g or m label.  Added unit tests. If memory is 0 an IllegalStateException is thrown. Updated unit tests to mock environment variables by subclassing SparkConf (tip provided by Josh Rosen).   Updated WorkerArguments to use SparkConf.getenv instead of System.getenv for reading the SPARK_WORKER_MEMORY environment variable.

Author: Bill Bejeck <bbejeck@gmail.com>

Closes #2309 from bbejeck/spark-memory-worker and squashes the following commits:

51cf915 [Bill Bejeck] SPARK-3178 - Validate the memory is greater than zero when set from the SPARK_WORKER_MEMORY environment variable or command line without a g or m label.  Added unit tests. If memory is 0 an IllegalStateException is thrown. Updated unit tests to mock environment variables by subclassing SparkConf (tip provided by Josh Rosen).   Updated WorkerArguments to use SparkConf.getenv instead of System.getenv for reading the SPARK_WORKER_MEMORY environment variable.
[SPARK-3946] gitignore in /python includes wrong directory

Modified to ignore not the docs/ directory, but only the docs/_build/ which is the output directory of sphinx build.

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #2796 from tsudukim/feature/SPARK-3946 and squashes the following commits:

2bea6a9 [Masayoshi TSUZUKI] [SPARK-3946] gitignore in /python includes wrong directory
[SPARK-3944][Core] Using Option[String] where value of String can be null

Author: shitis <ssaxena.ece@gmail.com>

Closes #2795 from Shiti/master and squashes the following commits:

46897d7 [shitis] Using Option Wrapper to convert String with value null to None
SPARK-3803 [MLLIB] ArrayIndexOutOfBoundsException found in executing computePrincipalComponents

Avoid overflow in computing n*(n+1)/2 as much as possible; throw explicit error when Gramian computation will fail due to negative array size; warn about large result when computing Gramian too

Author: Sean Owen <sowen@cloudera.com>

Closes #2801 from srowen/SPARK-3803 and squashes the following commits:

b4e6d92 [Sean Owen] Avoid overflow in computing n*(n+1)/2 as much as possible; throw explicit error when Gramian computation will fail due to negative array size; warn about large result when computing Gramian too
[SPARK-3869] ./bin/spark-class miss Java version with _JAVA_OPTIONS set

When _JAVA_OPTIONS environment variable is set, a command "java -version" outputs a message like "Picked up _JAVA_OPTIONS: -Dfile.encoding=UTF-8".
./bin/spark-class knows java version from the first line of "java -version" output, so it mistakes java version with _JAVA_OPTIONS set.

Author: cocoatomo <cocoatomo77@gmail.com>

Closes #2725 from cocoatomo/issues/3869-mistake-java-version and squashes the following commits:

f894ebd [cocoatomo] [SPARK-3869] ./bin/spark-class miss Java version with _JAVA_OPTIONS set
[SPARK-3943] Some scripts bin\*.cmd pollutes environment variables in Windows

Modified not to pollute environment variables.
Just moved the main logic into `XXX2.cmd` from `XXX.cmd`, and call `XXX2.cmd` with cmd command in `XXX.cmd`.
`pyspark.cmd` and `spark-class.cmd` are already using the same way, but `spark-shell.cmd`, `spark-submit.cmd` and `/python/docs/make.bat` are not.

Author: Masayoshi TSUZUKI <tsudukim@oss.nttdata.co.jp>

Closes #2797 from tsudukim/feature/SPARK-3943 and squashes the following commits:

b397a7d [Masayoshi TSUZUKI] [SPARK-3943] Some scripts bin\*.cmd pollutes environment variables in Windows
SPARK-1307 [DOCS] Don't use term 'standalone' to refer to a Spark Application

HT to Diana, just proposing an implementation of her suggestion, which I rather agreed with. Is there a second/third for the motion?

Refer to "self-contained" rather than "standalone" apps to avoid confusion with standalone deployment mode. And fix placement of reference to this in MLlib docs.

Author: Sean Owen <sowen@cloudera.com>

Closes #2787 from srowen/SPARK-1307 and squashes the following commits:

b5b82e2 [Sean Owen] Refer to "self-contained" rather than "standalone" apps to avoid confusion with standalone deployment mode. And fix placement of reference to this in MLlib docs.
[SPARK-2098] All Spark processes should support spark-defaults.conf, config file

This is another implementation about #1256
cc andrewor14 vanzin

Author: GuoQiang Li <witgo@qq.com>

Closes #2379 from witgo/SPARK-2098-new and squashes the following commits:

4ef1cbd [GuoQiang Li] review commit
49ef70e [GuoQiang Li] Refactor getDefaultPropertiesFile
c45d20c [GuoQiang Li] All Spark processes should support spark-defaults.conf, config file
[SPARK-3736] Workers reconnect when disassociated from the master.

Before, if the master node is killed and restarted, the worker nodes
would not attempt to reconnect to the Master. Therefore, when the Master
node was restarted, the worker nodes needed to be restarted as well.

Now, when the Master node is disconnected, the worker nodes will
continuously ping the master node in attempts to reconnect to it. Once
the master node restarts, it will detect one of the registration
requests from its former workers. The result is that the cluster
re-enters a healthy state.

In addition, when the master does not receive a heartbeat from the
worker, the worker was removed; however, when the worker sent a
heartbeat to the master, the master used to ignore the heartbeat. Now,
a master that receives a heartbeat from a worker that had been
disconnected will request the worker to re-attempt the registration
process, at which point the worker will send a RegisterWorker request
and be re-connected accordingly.

Re-connection attempts per worker are submitted every N seconds, where N
is configured by the property spark.worker.reconnect.interval - this has
a default of 60 seconds right now.