[SPARK-2461] [PySpark] Add a toString method to GeneralizedLinearModel

Add a toString method to GeneralizedLinearModel, also change `__str__` to `__repr__` for some classes, to provide better message in repr.

This PR is based on #1388, thanks to sryza!

closes #1388

Author: Sandy Ryza <sandy@cloudera.com>
Author: Davies Liu <davies.liu@gmail.com>

Closes #2625 from davies/string and squashes the following commits:

3544aad [Davies Liu] fix LinearModel
0bcd642 [Davies Liu] Merge branch 'sandy-spark-2461' of github.com:sryza/spark
1ce5c2d [Sandy Ryza] __repr__ back to __str__ in a couple places
aa9e962 [Sandy Ryza] Switch __str__ to __repr__
a0c5041 [Sandy Ryza] Add labels back in
1aa17f5 [Sandy Ryza] Match existing conventions
fac1bc4 [Sandy Ryza] Fix PEP8 error
f7b58ed [Sandy Ryza] SPARK-2461. Add a toString method to GeneralizedLinearModel
[SPARK-3786] [PySpark] speedup tests

This patch try to speed up tests of PySpark, re-use the SparkContext in tests.py and mllib/tests.py to reduce the overhead of create SparkContext, remove some test cases, which did not make sense. It also improve the performance of some cases, such as MergerTests and SortTests.

before this patch:

real	21m27.320s
user	4m42.967s
sys	0m17.343s

after this patch:

real	9m47.541s
user	2m12.947s
sys	0m14.543s

It almost cut the time by half.

Author: Davies Liu <davies.liu@gmail.com>

Closes #2646 from davies/tests and squashes the following commits:

c54de60 [Davies Liu] revert change about memory limit
6a2a4b0 [Davies Liu] refactor of tests, speedup 100%
[SPARK-3773][PySpark][Doc] Sphinx build warning

When building Sphinx documents for PySpark, we have 12 warnings.
Their causes are almost docstrings in broken ReST format.

To reproduce this issue, we should run following commands on the commit: 6e27cb630de69fa5acb510b4e2f6b980742b1957.

```bash
$ cd ./python/docs
$ make clean html
...
/Users/<user>/MyRepos/Scala/spark/python/pyspark/__init__.py:docstring of pyspark.SparkContext.sequenceFile:4: ERROR: Unexpected indentation.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/__init__.py:docstring of pyspark.RDD.saveAsSequenceFile:4: ERROR: Unexpected indentation.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/classification.py:docstring of pyspark.mllib.classification.LogisticRegressionWithSGD.train:14: ERROR: Unexpected indentation.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/classification.py:docstring of pyspark.mllib.classification.LogisticRegressionWithSGD.train:16: WARNING: Definition list ends without a blank line; unexpected unindent.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/classification.py:docstring of pyspark.mllib.classification.LogisticRegressionWithSGD.train:17: WARNING: Block quote ends without a blank line; unexpected unindent.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/classification.py:docstring of pyspark.mllib.classification.SVMWithSGD.train:14: ERROR: Unexpected indentation.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/classification.py:docstring of pyspark.mllib.classification.SVMWithSGD.train:16: WARNING: Definition list ends without a blank line; unexpected unindent.
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/classification.py:docstring of pyspark.mllib.classification.SVMWithSGD.train:17: WARNING: Block quote ends without a blank line; unexpected unindent.
/Users/<user>/MyRepos/Scala/spark/python/docs/pyspark.mllib.rst:50: WARNING: missing attribute mentioned in :members: or __all__: module pyspark.mllib.regression, attribute RidgeRegressionModelLinearRegressionWithSGD
/Users/<user>/MyRepos/Scala/spark/python/pyspark/mllib/tree.py:docstring of pyspark.mllib.tree.DecisionTreeModel.predict:3: ERROR: Unexpected indentation.
...
checking consistency... /Users/<user>/MyRepos/Scala/spark/python/docs/modules.rst:: WARNING: document isn't included in any toctree
...
copying static files... WARNING: html_static_path entry u'/Users/<user>/MyRepos/Scala/spark/python/docs/_static' does not exist
...
build succeeded, 12 warnings.
```

Author: cocoatomo <cocoatomo77@gmail.com>

Closes #2653 from cocoatomo/issues/3773-sphinx-build-warnings and squashes the following commits:

6f65661 [cocoatomo] [SPARK-3773][PySpark][Doc] Sphinx build warning
[SPARK-3479] [Build] Report failed test category

This PR allows SparkQA (i.e. Jenkins) to report in its posts to GitHub what category of test failed, if one can be determined.

The failure categories are:
* general failure
* RAT checks failed
* Scala style checks failed
* Python style checks failed
* Build failed
* Spark unit tests failed
* PySpark unit tests failed
* MiMa checks failed

This PR also fixes the diffing logic used to determine if a patch introduces new classes.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #2606 from nchammas/report-failed-test-category and squashes the following commits:

d67df03 [Nicholas Chammas] report what test category failed
[SPARK-3627] - [yarn] - fix exit code and final status reporting to RM

See the description and whats handled in the jira comment: https://issues.apache.org/jira/browse/SPARK-3627?focusedCommentId=14150013&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14150013

This does not handle yarn client mode reporting of the driver to the AM.   I think that should be handled when we make it an unmanaged AM.

Author: Thomas Graves <tgraves@apache.org>

Closes #2577 from tgravescs/SPARK-3627 and squashes the following commits:

9c2efbf [Thomas Graves] review comments
e8cc261 [Thomas Graves] fix accidental typo during fixing comment
24c98e3 [Thomas Graves] rework
85f1901 [Thomas Graves] Merge remote-tracking branch 'upstream/master' into SPARK-3627
fab166d [Thomas Graves] update based on review comments
32f4dfa [Thomas Graves] switch back
f0b6519 [Thomas Graves] change order of cleanup staging dir
d3cc800 [Thomas Graves] SPARK-3627 - yarn - fix exit code and final status reporting to RM
[SPARK-3827] Very long RDD names are not rendered properly in web UI

With Spark SQL we generate very long RDD names. These names are not properly rendered in the web UI.

This PR fixes the rendering issue.

[SPARK-3827] #comment Linking PR with JIRA

Author: Hossein <hossein@databricks.com>

Closes #2687 from falaki/sparkTableUI and squashes the following commits:

fd06409 [Hossein] Limit width of cell when RDD name is too long
[SPARK-3808] PySpark fails to start in Windows

Modified syntax error of *.cmd script.

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

Closes #2669 from tsudukim/feature/SPARK-3808 and squashes the following commits:

7f804e6 [Masayoshi TSUZUKI] [SPARK-3808] PySpark fails to start in Windows
[SPARK-3762] clear reference of SparkEnv after stop

SparkEnv is cached in ThreadLocal object, so after stop and create a new SparkContext, old SparkEnv is still used by some threads, it will trigger many problems, for example, pyspark will have problem after restart SparkContext, because py4j use thread pool for RPC.

This patch will clear all the references after stop a SparkEnv.

cc mateiz tdas pwendell

Author: Davies Liu <davies.liu@gmail.com>

Closes #2624 from davies/env and squashes the following commits:

a69f30c [Davies Liu] deprecate getThreadLocal
ba77ca4 [Davies Liu] remove getThreadLocal(), update docs
ee62bb7 [Davies Liu] cleanup ThreadLocal of SparnENV
4d0ea8b [Davies Liu] clear reference of SparkEnv after stop
[SPARK-3731] [PySpark] fix memory leak in PythonRDD

The parent.getOrCompute() of PythonRDD is executed in a separated thread, it should release the memory reserved for shuffle and unrolling finally.

Author: Davies Liu <davies.liu@gmail.com>

Closes #2668 from davies/leak and squashes the following commits:

ae98be2 [Davies Liu] fix memory leak in PythonRDD
[SPARK-3825] Log more detail when unrolling a block fails

Before:
```
14/10/06 16:45:42 WARN CacheManager: Not enough space to cache partition rdd_0_2
in memory! Free memory is 481861527 bytes.
```
After:
```
14/10/07 11:08:24 WARN MemoryStore: Not enough space to cache rdd_2_0 in memory!
(computed 68.8 MB so far)
14/10/07 11:08:24 INFO MemoryStore: Memory use = 1088.0 B (blocks) + 445.1 MB
(scratch space shared across 8 thread(s)) = 445.1 MB. Storage limit = 459.5 MB.
```

Author: Andrew Or <andrewor14@gmail.com>

Closes #2688 from andrewor14/cache-log-message and squashes the following commits:

28e33d6 [Andrew Or] Shy away from "unrolling"
5638c49 [Andrew Or] Grammar
39a0c28 [Andrew Or] Log more detail when unrolling a block fails
[SPARK-3777] Display "Executor ID" for Tasks in Stage page

Now the Stage page only displays "Executor"(host) for tasks. However, there may be more than one Executors running in the same host. Currently, when some task is hung, I only know the host of the faulty executor. Therefore I have to check all executors in the host.

Adding "Executor ID" in the Tasks table. would be helpful to locate the faulty executor. Here is the new page:

![add_executor_id_for_tasks](https://cloud.githubusercontent.com/assets/1000778/4505774/acb9648c-4afa-11e4-8826-8768a0a60cc9.png)

Author: zsxwing <zsxwing@gmail.com>

Closes #2642 from zsxwing/SPARK-3777 and squashes the following commits:

37945af [zsxwing] Put Executor ID and Host into one cell
4bbe2c7 [zsxwing] [SPARK-3777] Display "Executor ID" for Tasks in Stage page
Added abstract TestParams class for mllib example parameters
Merge remote-tracking branch 'upstream/master' into dtrunner-update