[SPARK-2993] [MLLib] colStats (wrapper around MultivariateStatisticalSummary) in Statistics

[dorx]

For both Scala and Python.

The ser/de util functions were moved out of PythonMLLibAPI and into their own object to avoid creating the PythonMLLibAPI object inside of MultivariateStatisticalSummarySerialized, which is then referenced inside of a method in PythonMLLibAPI.

MultivariateStatisticalSummarySerialized was created to serialize the Vector fields in MultivariateStatisticalSummary.

[SparkQA]

QA tests have started for PR 1911. This patch merges cleanly.
View progress: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18392/consoleFull

[SparkQA]

QA results for PR 1911:
- This patch FAILED unit tests.
- This patch merges cleanly
- This patch adds the following public classes (experimental):
class MultivariateStatisticalSummarySerialized(val summary: MultivariateStatisticalSummary)
class MultivariateStatisticalSummary(object):

For more information see test ouptut:
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18392/consoleFull

[mengxr]

@DeveloperApi?

[SparkQA]

QA tests have started for PR 1911. This patch merges cleanly.
View progress: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18397/consoleFull

[SparkQA]

QA results for PR 1911:
- This patch PASSES unit tests.
- This patch merges cleanly
- This patch adds the following public classes (experimental):
class MultivariateStatisticalSummarySerialized(val summary: MultivariateStatisticalSummary)
class MultivariateStatisticalSummary(object):

For more information see test ouptut:
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18397/consoleFull

[SparkQA]

QA tests have started for PR 1911. This patch merges cleanly.
View progress: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18412/consoleFull

[SparkQA]

QA results for PR 1911:
- This patch FAILED unit tests.
- This patch merges cleanly
- This patch adds the following public classes (experimental):
class MultivariateStatisticalSummarySerialized(val summary: MultivariateStatisticalSummary)
class MultivariateStatisticalSummary(object):

For more information see test ouptut:
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18412/consoleFull

[dorx]

Jenkins, retest this please.

[SparkQA]

QA tests have started for PR 1911. This patch merges cleanly.
View progress: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18414/consoleFull

[SparkQA]

QA results for PR 1911:
- This patch PASSES unit tests.
- This patch merges cleanly
- This patch adds the following public classes (experimental):
class MultivariateStatisticalSummarySerialized(val summary: MultivariateStatisticalSummary)
class MultivariateStatisticalSummary(object):

For more information see test ouptut:
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18414/consoleFull

[mengxr]

LGTM. Merged into both master and branch-1.1. Thanks for adding this and cleaning MLLibPythonAPI!!