[SPARK-17462][MLLIB]use VersionUtils to parse Spark version strings

## What changes were proposed in this pull request?

Several places in MLlib use custom regexes or other approaches to parse Spark versions.
Those should be fixed to use the VersionUtils. This PR replaces custom regexes with
VersionUtils to get Spark version numbers.
## How was this patch tested?

Existing tests.

Signed-off-by: VinceShieh vincent.xieintel.com

Author: VinceShieh <vincent.xie@intel.com>

Closes #15055 from VinceShieh/SPARK-17462.

(cherry picked from commit de77c677)
Signed-off-by: Sean Owen <sowen@cloudera.com>

mllib/src/main/scala/org/apache/spark/ml/clustering/KMeans.scala

@@ -33,6 +33,7 @@ import org.apache.spark.rdd.RDD
 import org.apache.spark.sql.{DataFrame, Dataset, Row}
 import org.apache.spark.sql.functions.{col, udf}
 import org.apache.spark.sql.types.{IntegerType, StructType}
+import org.apache.spark.util.VersionUtils.majorVersion
 
 /**
  * Common params for KMeans and KMeansModel
@@ -232,10 +233,7 @@ object KMeansModel extends MLReadable[KMeansModel] {
       val metadata = DefaultParamsReader.loadMetadata(path, sc, className)
       val dataPath = new Path(path, "data").toString
 
-      val versionRegex = "([0-9]+)\\.(.+)".r
-      val versionRegex(major, _) = metadata.sparkVersion
-
-      val clusterCenters = if (major.toInt >= 2) {
+      val clusterCenters = if (majorVersion(metadata.sparkVersion) >= 2) {
         val data: Dataset[Data] = sparkSession.read.parquet(dataPath).as[Data]
         data.collect().sortBy(_.clusterIdx).map(_.clusterCenter).map(OldVectors.fromML)
       } else {

mllib/src/main/scala/org/apache/spark/ml/feature/PCA.scala

@@ -34,6 +34,7 @@ import org.apache.spark.rdd.RDD
 import org.apache.spark.sql._
 import org.apache.spark.sql.functions._
 import org.apache.spark.sql.types.{StructField, StructType}
+import org.apache.spark.util.VersionUtils.majorVersion
 
 /**
  * Params for [[PCA]] and [[PCAModel]].
@@ -204,11 +205,8 @@ object PCAModel extends MLReadable[PCAModel] {
     override def load(path: String): PCAModel = {
       val metadata = DefaultParamsReader.loadMetadata(path, sc, className)
 
-      val versionRegex = "([0-9]+)\\.(.+)".r
-      val versionRegex(major, _) = metadata.sparkVersion
-
       val dataPath = new Path(path, "data").toString
-      val model = if (major.toInt >= 2) {
+      val model = if (majorVersion(metadata.sparkVersion) >= 2) {
         val Row(pc: DenseMatrix, explainedVariance: DenseVector) =
           sparkSession.read.parquet(dataPath)
             .select("pc", "explainedVariance")