[SPARK-9118][ML]: Implement IntArrayParam in mllib

[rekhajoshm]

Implement IntArrayParam in mllib

[SparkQA]

Test build #37667 has finished for PR 7481 at commit d3b1766.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class IntArrayParam(parent: Params, name: String, doc: String, isValid: Array[Int] => Boolean)

[mengxr]

LGTM. Merged into master. Thanks! (It would be better to implement this when we really need it.)

[rekhajoshm]

thanks @mengxr