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
[SPARK-2852][MLLIB] Separate model from IDF/StandardScaler algorithms

This is part of SPARK-2828:

1. separate IDF model from IDF algorithm (which generates a model)
2. separate StandardScaler model from StandardScaler

CC: dbtsai

Author: Xiangrui Meng <meng@databricks.com>

Closes #1814 from mengxr/feature-api-update and squashes the following commits:

40d863b [Xiangrui Meng] move mean and variance to model
48a0fff [Xiangrui Meng] separate Model from StandardScaler algorithm
89f3486 [Xiangrui Meng] update IDF to separate Model from Algorithm
Fix bug: escape escaped backslashes and quotes properly...

This is so that the way this is parsed and the way Java parses
its java opts is consistent.
escape -> split (minor)
SPARK-2905 Fixed path sbin => bin

Author: Oleg Danilov <oleg.danilov@wandisco.com>

Closes #1835 from dosoft/SPARK-2905 and squashes the following commits:

4df423c [Oleg Danilov] SPARK-2905 Fixed path sbin => bin
SPARK-2899 Doc generation is back to working in new SBT Build.

The reason for this bug was introduciton of OldDeps project. It had to be excluded to prevent unidocs from trying to put it on "docs compile" classpath.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #1830 from ScrapCodes/doc-fix and squashes the following commits:

e5d52e6 [Prashant Sharma] SPARK-2899 Doc generation is back to working in new SBT Build.
Escape spark.*.extraJavaOptions correctly

We previously never dealt with this correctly, in that we evaluated
all backslashes twice, once when passing spark.*.extraJavaOptions
into SparkSubmit, and another time when calling
Utils.splitCommandString.

This means we need to pass the raw values of these configs directly
to the JVM without evaluating the backslashes when launching
SparkSubmit. The way we do this is through a few custom environment
variables.

As of this commit, the user should follow the format outlined in
spark-defaults.conf.template for spark.*.extraJavaOptions, and
the expected java options (with quotes, whitespaces and backslashes
and everything) will be propagated to the driver or the executors
correctly.
Minor changes to spark-defaults.conf.template

... to highlight our new-found ability to deal with special values.
Merge branch 'master' of github.com:apache/spark into submit-driver-extra