Minor cleanup of code.

Author: Reynold Xin <rxin@apache.org>

Closes #2581 from rxin/minor-cleanup and squashes the following commits:

736a91b [Reynold Xin] Minor cleanup of code.
[SPARK-3613] Record only average block size in MapStatus for large stages

This changes the way we send MapStatus from executors back to driver for large stages (>2000 tasks). For large stages, we no longer send one byte per block. Instead, we just send the average block size.

This makes large jobs (tens of thousands of tasks) much more reliable since the driver no longer sends huge amount of data.

Author: Reynold Xin <rxin@apache.org>

Closes #2470 from rxin/mapstatus and squashes the following commits:

822ff54 [Reynold Xin] Code review feedback.
3b86f56 [Reynold Xin] Added MimaExclude.
f89d182 [Reynold Xin] Fixed a bug in MapStatus
6a0401c [Reynold Xin] [SPARK-3613] Record only average block size in MapStatus for large stages.
[SPARK-3709] Executors don't always report broadcast block removal properly back to the driver

The problem was that the 2nd argument in RemoveBroadcast is not tellMaster! It is "removeFromDriver". Basically when removeFromDriver is not true, we don't report broadcast block removal back to the driver, and then other executors mistakenly think that the executor would still have the block, and try to fetch from it.

cc @tdas

Author: Reynold Xin <rxin@apache.org>

Closes #2588 from rxin/debug and squashes the following commits:

6dab2e3 [Reynold Xin] Don't log random messages.
f430686 [Reynold Xin] Always report broadcast removal back to master.
2a13f70 [Reynold Xin] iii
[SPARK-3734] DriverRunner should not read SPARK_HOME from submitter's environment

When using spark-submit in `cluster` mode to submit a job to a Spark Standalone
cluster, if the JAVA_HOME environment variable was set on the submitting
machine then DriverRunner would attempt to use the submitter's JAVA_HOME to
launch the driver process (instead of the worker's JAVA_HOME), causing the
driver to fail unless the submitter and worker had the same Java location.

This commit fixes this by reading JAVA_HOME from sys.env instead of
command.environment.

Author: Josh Rosen <joshrosen@apache.org>

Closes #2586 from JoshRosen/SPARK-3734 and squashes the following commits:

e9513d9 [Josh Rosen] [SPARK-3734] DriverRunner should not read SPARK_HOME from submitter's environment.
Revert "[SPARK-3007][SQL]Add Dynamic Partition support to Spark Sql hive"

This reverts commit 0bbe7faeffa17577ae8a33dfcd8c4c783db5c909.
HOTFIX: Ignore flaky tests in YARN
[SPARK-3356] [DOCS] Document when RDD elements' ordering within partitions is nondeterministic

As suggested by mateiz , and because it came up on the mailing list again last week, this attempts to document that ordering of elements is not guaranteed across RDD evaluations in groupBy, zip, and partition-wise RDD methods. Suggestions welcome about the wording, or other methods that need a note.

Author: Sean Owen <sowen@cloudera.com>

Closes #2508 from srowen/SPARK-3356 and squashes the following commits:

b7c96fd [Sean Owen] Undo change to programming guide
ad4aeec [Sean Owen] Don't mention ordering in partition-wise methods, reword description of ordering for zip methods per review, and add similar note to programming guide, which mentions groupByKey (but not zip methods)
fce943b [Sean Owen] Note that ordering of elements is not guaranteed across RDD evaluations in groupBy, zip, and partition-wise RDD methods
SPARK-2621. Update task InputMetrics incrementally
Fall back to split size
Add missing curly braces
Switch from pull to push model and add test