[SPARK-14239] [ML] Add load for LDAModel that supports both local and distributedMode

[hhbyyh]

What changes were proposed in this pull request?

Add load for LDAModel that supports loading both local and distributedModel, as discussed in #9894. So that users don't have to know the details.

How was this patch tested?

Unit tests

[SparkQA]

Test build #54440 has finished for PR 12037 at commit 0ba310e.

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

[SparkQA]

Test build #72512 has finished for PR 12037 at commit 0ba310e.

• This patch fails SparkR unit tests.
• This patch does not merge cleanly.
• This patch adds no public classes.

[hhbyyh]

Closing stale PR.