[SPARK-14444][BUILD] Add a new scalastyle `NoScalaDoc` to prevent ScalaDoc-style multiline comments

## What changes were proposed in this pull request?

According to the [Spark Code Style Guide](https://cwiki.apache.org/confluence/display/SPARK/Spark+Code+Style+Guide#SparkCodeStyleGuide-Indentation), this PR adds a new scalastyle rule to prevent the followings.
```
/** In Spark, we don't use the ScalaDoc style so this
  * is not correct.
  */
```

## How was this patch tested?

Pass the Jenkins tests (including `lint-scala`).

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12221 from dongjoon-hyun/SPARK-14444.

1 files changed, 6 insertions, 4 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/mllib/stat/distribution/MultivariateGaussian.scala b/mllib/src/main/scala/org/apache/spark/mllib/stat/distribution/MultivariateGaussian.scala
index 052b5b1d65..6c6e9fb7c6 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/stat/distribution/MultivariateGaussian.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/stat/distribution/MultivariateGaussian.scala
@@ -61,15 +61,17 @@ class MultivariateGaussian @Since("1.3.0") (
    */
   private val (rootSigmaInv: DBM[Double], u: Double) = calculateCovarianceConstants
 
-  /** Returns density of this multivariate Gaussian at given point, x
-    */
+  /**
+   * Returns density of this multivariate Gaussian at given point, x
+   */
    @Since("1.3.0")
   def pdf(x: Vector): Double = {
     pdf(x.toBreeze)
   }
 
-  /** Returns the log-density of this multivariate Gaussian at given point, x
-    */
+  /**
+   * Returns the log-density of this multivariate Gaussian at given point, x
+   */
    @Since("1.3.0")
   def logpdf(x: Vector): Double = {
     logpdf(x.toBreeze)