[SPARK-18240][ML][PySpark] Add Summary of BiKMeans and GMM in pyspark

[zhengruifeng]

What changes were proposed in this pull request?

1, create class ClusteringSummary
2, add summary of BiKMeans and GMM by extends ClusteringSummary
3, remove two unused imports

How was this patch tested?

added tests in clustering.py and local tests in pyspark

[SparkQA]

Test build #68051 has finished for PR 15748 at commit 5395e2a.

• This patch fails PySpark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #68062 has finished for PR 15748 at commit dbf883b.

• This patch fails PySpark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #68063 has finished for PR 15748 at commit 5b5e729.

• This patch fails PySpark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #68064 has finished for PR 15748 at commit 332d8d6.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[zhengruifeng]

@yanboliang @jkbradley Could you please make a review?

[jkbradley]

I do want to add this at some point, though we need to focus on QA for now

[zhengruifeng]

@jkbradley There is somewhat misunderstanding. I close this PR because there is a similar one. Sethah created SPARK-18282 just one day after this one. And people reviewed that one. So I think it's better to close this PR, and Sethah take it over. I will also help to reveiw that PR and QA. ☺