[SPARK-13786][ML][PYTHON] Removed save/load for python tuning

[jkbradley]

What changes were proposed in this pull request?

Per discussion on [https://github.com//pull/12604], this removes ML persistence for Python tuning (TrainValidationSplit, CrossValidator, and their Models) since they do not handle nesting easily. This support should be re-designed and added in the next release.

How was this patch tested?

Removed unit test elements saving and loading the tuning algorithms, but kept tests to save and load their bestModel fields.

[jkbradley]

Rebased to fix conflicts

[SparkQA]

Test build #57352 has finished for PR 12782 at commit d70bfcb.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class CrossValidator(Estimator, ValidatorParams):
  • class CrossValidatorModel(Model, ValidatorParams):
  • class TrainValidationSplit(Estimator, ValidatorParams):
  • class TrainValidationSplitModel(Model, ValidatorParams):

[SparkQA]

Test build #57351 has finished for PR 12782 at commit a91f39e.

• This patch passes all tests.
• This patch does not merge cleanly.
• This patch adds the following public classes (experimental):
  • class CrossValidator(Estimator, ValidatorParams):
  • class CrossValidatorModel(Model, ValidatorParams):
  • class TrainValidationSplit(Estimator, ValidatorParams):
  • class TrainValidationSplitModel(Model, ValidatorParams):

[jkbradley]

Rebased to fix apparent unclean merge

[SparkQA]

Test build #57361 has finished for PR 12782 at commit 6df120f.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class CrossValidator(Estimator, ValidatorParams):
  • class CrossValidatorModel(Model, ValidatorParams):
  • class TrainValidationSplit(Estimator, ValidatorParams):
  • class TrainValidationSplitModel(Model, ValidatorParams):

[jkbradley]

@yinxusen Would you mind taking a look? Thank you!

[thunterdb]

do you need to have a wildcard import?

[jkbradley]

There are ~5 imports, so I think it's worthwhile.

[thunterdb]

@jkbradley this looks good to me

[mengxr]

Merged into master. Thanks!

[jkbradley]

Thanks!