[SPARK-2852][MLLIB] API consistency for `mllib.feature`

This is part of SPARK-2828:

1. added a Java-friendly fit method to Word2Vec with tests
2. change DeveloperApi to Experimental for Normalizer & StandardScaler
3. change default feature dimension to 2^20 in HashingTF

Author: Xiangrui Meng <meng@databricks.com>

Closes #1807 from mengxr/feature-api-check and squashes the following commits:

773c1a9 [Xiangrui Meng] change default numFeatures to 2^20 in HashingTF change annotation from DeveloperApi to Experimental in Normalizer and StandardScaler
883e122 [Xiangrui Meng] add @Experimental to Word2VecModel add a Java-friendly method to Word2Vec.fit with tests
[PySpark] Add blanklines to Python docstrings so example code renders correctly

Author: RJ Nowling <rnowling@gmail.com>

Closes #1808 from rnowling/pyspark_docs and squashes the following commits:

c06d774 [RJ Nowling] Add blanklines to Python docstrings so example code renders correctly
[HOTFIX][Streaming] Handle port collisions in flume polling test

This is failing my tests in #1777. @tdas

Author: Andrew Or <andrewor14@gmail.com>

Closes #1803 from andrewor14/fix-flaky-streaming-test and squashes the following commits:

ea11a03 [Andrew Or] Catch all exceptions caused by BindExceptions
54a0ca0 [Andrew Or] Merge branch 'master' of github.com:apache/spark into fix-flaky-streaming-test
664095c [Andrew Or] Tone down bind exception message
af3ddc9 [Andrew Or] Handle port collisions in flume polling test
SPARK-2882: Spark build now checks local maven cache for dependencies

Fixes [SPARK-2882](https://issues.apache.org/jira/browse/SPARK-2882)

Author: Gregory Owen <greowen@gmail.com>

Closes #1818 from GregOwen/spark-2882 and squashes the following commits:

294446d [Gregory Owen] SPARK-2882: Spark build now checks local maven cache for dependencies
[SPARK-2583] ConnectionManager error reporting

This patch modifies the ConnectionManager so that error messages are sent in reply when uncaught exceptions occur during message processing.  This prevents message senders from hanging while waiting for an acknowledgment if the remote message processing failed.

This is an updated version of sarutak's PR, #1490.  The main change is to use Futures / Promises to signal errors.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>
Author: Josh Rosen <joshrosen@apache.org>

Closes #1758 from JoshRosen/connection-manager-fixes and squashes the following commits:

68620cb [Josh Rosen] Fix test in BlockFetcherIteratorSuite:
83673de [Josh Rosen] Error ACKs should trigger IOExceptions, so catch only those exceptions in the test.
b8bb4d4 [Josh Rosen] Fix manager.id vs managerServer.id typo that broke security tests.
659521f [Josh Rosen] Include previous exception when throwing new one
a2f745c [Josh Rosen] Remove sendMessageReliablySync; callers can wait themselves.
c01c450 [Josh Rosen] Return Try[Message] from sendMessageReliablySync.
f1cd1bb [Josh Rosen] Clean up @sarutak's PR #1490 for [SPARK-2583]: ConnectionManager error reporting
7399c6b [Josh Rosen] Merge remote-tracking branch 'origin/pr/1490' into connection-manager-fixes
ee91bb7 [Kousuke Saruta] Modified BufferMessage.scala to keep the spark code style
9dfd0d8 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
e7d9aa6 [Kousuke Saruta] rebase to master
326a17f [Kousuke Saruta] Add test cases to ConnectionManagerSuite.scala for SPARK-2583
2a18d6b [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
22d7ebd [Kousuke Saruta] Add test cases to BlockManagerSuite for SPARK-2583
e579302 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
281589c [Kousuke Saruta] Add a test case to BlockFetcherIteratorSuite.scala for fetching block from remote from successfully
0654128 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
ffaa83d [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
12d3de8 [Kousuke Saruta] Added BlockFetcherIteratorSuite.scala
4117b8f [Kousuke Saruta] Modified ConnectionManager to be alble to handle error during processing message
717c9c3 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
6635467 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into SPARK-2583
e2b8c4a [Kousuke Saruta] Modify to propagete error using ConnectionManager
SPARK-2879 [BUILD] Use HTTPS to access Maven Central and other repos

Maven Central has just now enabled HTTPS access for everyone to Maven Central (http://central.sonatype.org/articles/2014/Aug/03/https-support-launching-now/) This is timely, as a reminder of how easily an attacker can slip malicious code into a build that's downloading artifacts over HTTP (http://blog.ontoillogical.com/blog/2014/07/28/how-to-take-over-any-java-developer/).

In the meantime, it looks like the Spring repo also now supports HTTPS, so can be used this way too.

I propose to use HTTPS to access these repos.

Author: Sean Owen <srowen@gmail.com>

Closes #1805 from srowen/SPARK-2879 and squashes the following commits:

7043a8e [Sean Owen] Use HTTPS for Maven Central libs and plugins; use id 'central' to override parent properly; use HTTPS for Spring repo
HOTFIX: Support custom Java 7 location
[SPARK-2887] fix bug of countApproxDistinct() when have more than one partition

fix bug of countApproxDistinct() when have more than one partition

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

Closes #1812 from davies/approx and squashes the following commits:

bf757ce [Davies Liu] fix bug of countApproxDistinct() when have more than one partition
[SPARK-2851] [mllib] DecisionTree Python consistency update

Added 6 static train methods to match Python API, but without default arguments (but with Python default args noted in docs).

Added factory classes for Algo and Impurity, but made private[mllib].

CC: mengxr dorx  Please let me know if there are other changes which would help with API consistency---thanks!

Author: Joseph K. Bradley <joseph.kurata.bradley@gmail.com>

Closes #1798 from jkbradley/dt-python-consistency and squashes the following commits:

6f7edf8 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dt-python-consistency
a0d7dbe [Joseph K. Bradley] DecisionTree: In Java-friendly train* methods, changed to use JavaRDD instead of RDD.
ee1d236 [Joseph K. Bradley] DecisionTree API updates: * Removed train() function in Python API (tree.py) ** Removed corresponding function in Scala/Java API (the ones taking basic types)
00f820e [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dt-python-consistency
fe6dbfa [Joseph K. Bradley] removed unnecessary imports
e358661 [Joseph K. Bradley] DecisionTree API change: * Added 6 static train methods to match Python API, but without default arguments (but with Python default args noted in docs).
c699850 [Joseph K. Bradley] a few doc comments
eaf84c0 [Joseph K. Bradley] Added DecisionTree static train() methods API to match Python, but without default parameters
SPARK-2879 part 2 [BUILD] Use HTTPS to access Maven Central and other repos

.. and use canonical repo1.maven.org Maven Central repo. (And make sure snapshots are disabled for plugins from Maven Central.)

Author: Sean Owen <srowen@gmail.com>

Closes #1828 from srowen/SPARK-2879.2 and squashes the following commits:

639f495 [Sean Owen] .. and use canonical repo1.maven.org Maven Central repo. (And make sure snapshots are disabled for plugins from Maven Central.)
[mllib] DecisionTree Strategy parameter checks

Added some checks to Strategy to print out meaningful error messages when given invalid DecisionTree parameters.
CC mengxr

Author: Joseph K. Bradley <joseph.kurata.bradley@gmail.com>

Closes #1821 from jkbradley/dt-robustness and squashes the following commits:

4dc449a [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dt-robustness
7a61f7b [Joseph K. Bradley] Added some checks to Strategy to print out meaningful error messages when given invalid DecisionTree parameters