[SPARK-14152] [ML] [PySpark] MultilayerPerceptronClassifier supports save/load for Python API

[yanboliang]

What changes were proposed in this pull request?

MultilayerPerceptronClassifier supports save/load for Python API.

How was this patch tested?

doctest.

cc @mengxr @jkbradley @yinxusen

[SparkQA]

Test build #54156 has finished for PR 11952 at commit 6b4830a.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class MultilayerPerceptronClassificationModel(JavaModel, JavaMLWritable, JavaMLReadable):

[yinxusen]

LGTM

[jkbradley]

LGTM
I'll just re-run tests quickly before merging

[SparkQA]

Test build #2711 has finished for PR 11952 at commit 6b4830a.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class MultilayerPerceptronClassificationModel(JavaModel, JavaMLWritable, JavaMLReadable):

[jkbradley]

spurious failure

[SparkQA]

Test build #2714 has finished for PR 11952 at commit 6b4830a.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class MultilayerPerceptronClassificationModel(JavaModel, JavaMLWritable, JavaMLReadable):

[jkbradley]

Merging with master
Thanks!