[SPARK-16137][SPARKR] randomForest for R

[felixcheung]

What changes were proposed in this pull request?

Random Forest Regression and Classification for R
Clean-up/reordering generics.R

How was this patch tested?

manual tests, unit tests

[SparkQA]

Test build #67438 has finished for PR 15607 at commit 7d6e605.

• This patch fails some tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class RandomForestClassifierWrapperWriter(instance: RandomForestClassifierWrapper)
  • class RandomForestClassifierWrapperReader extends MLReader[RandomForestClassifierWrapper]
  • class RandomForestRegressorWrapperWriter(instance: RandomForestRegressorWrapper)
  • class RandomForestRegressorWrapperReader extends MLReader[RandomForestRegressorWrapper]

[SparkQA]

Test build #67441 has finished for PR 15607 at commit 4442abe.

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

[felixcheung]

Hmm, it works fine with
roxygen2 "roxygen2" "/usr/local/lib/R/site-library" "5.0.1"

maybe it is the older version on Jenkins?

First time using roxygen2 4.0. Upgrading automatically...
Error: Failure in roxygen block beginning mllib.R:1449
Mismatched braces: "@param featureSubsetStrategy The number of features to consider for splits at each tree node.
       See
\href{http://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.ml.classification.RandomForestClassifier"
Execution halted

[SparkQA]

Test build #67442 has finished for PR 15607 at commit b44dada.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #67443 has finished for PR 15607 at commit 0b9fa4f.

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

[SparkQA]

Test build #67476 has finished for PR 15607 at commit 19ad285.

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

[felixcheung]

@yanboliang @mengxr would love your review. thanks.

[SparkQA]

Test build #67628 has finished for PR 15607 at commit a4081d4.

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

[SparkQA]

Test build #67629 has finished for PR 15607 at commit 96ce6a5.

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

[felixcheung]

merged to master.