[MINOR] Add missing sc.stop() to end of examples

## What changes were proposed in this pull request?

Add `finally` clause for `sc.stop()` in the `test("register and deregister Spark listener from SparkContext")`.

## How was this patch tested?
Pass the build and unit tests.

Author: Weiqing Yang <yangweiqing001@gmail.com>

Closes #16426 from weiqingy/testIssue.

core/src/test/scala/org/apache/spark/SparkContextSuite.scala

@@ -455,16 +455,14 @@ class SparkContextSuite extends SparkFunSuite with LocalSparkContext {
 
   test("register and deregister Spark listener from SparkContext") {
     sc = new SparkContext(new SparkConf().setAppName("test").setMaster("local"))
-    try {
-      val sparkListener1 = new SparkListener { }
-      val sparkListener2 = new SparkListener { }
-      sc.addSparkListener(sparkListener1)
-      sc.addSparkListener(sparkListener2)
-      assert(sc.listenerBus.listeners.contains(sparkListener1))
-      assert(sc.listenerBus.listeners.contains(sparkListener2))
-      sc.removeSparkListener(sparkListener1)
-      assert(!sc.listenerBus.listeners.contains(sparkListener1))
-      assert(sc.listenerBus.listeners.contains(sparkListener2))
-    }
+    val sparkListener1 = new SparkListener { }
+    val sparkListener2 = new SparkListener { }
+    sc.addSparkListener(sparkListener1)
+    sc.addSparkListener(sparkListener2)
+    assert(sc.listenerBus.listeners.contains(sparkListener1))
+    assert(sc.listenerBus.listeners.contains(sparkListener2))
+    sc.removeSparkListener(sparkListener1)
+    assert(!sc.listenerBus.listeners.contains(sparkListener1))
+    assert(sc.listenerBus.listeners.contains(sparkListener2))
   }
 }

examples/src/main/java/org/apache/spark/examples/mllib/JavaBinaryClassificationMetricsExample.java

@@ -111,5 +111,7 @@ public class JavaBinaryClassificationMetricsExample {
     model.save(sc, "target/tmp/LogisticRegressionModel");
     LogisticRegressionModel.load(sc, "target/tmp/LogisticRegressionModel");
     // $example off$
+
+    sc.stop();
   }
 }

examples/src/main/java/org/apache/spark/examples/mllib/JavaLBFGSExample.java

@@ -103,6 +103,8 @@ public class JavaLBFGSExample {
       System.out.println(l);
     System.out.println("Area under ROC = " + auROC);
     // $example off$
+
+    sc.stop();
   }
 }
 

examples/src/main/java/org/apache/spark/examples/mllib/JavaMulticlassClassificationMetricsExample.java

@@ -91,5 +91,7 @@ public class JavaMulticlassClassificationMetricsExample {
     LogisticRegressionModel sameModel = LogisticRegressionModel.load(sc,
       "target/tmp/LogisticRegressionModel");
     // $example off$
+
+    sc.stop();
   }
 }

examples/src/main/java/org/apache/spark/examples/mllib/JavaPCAExample.java

@@ -61,5 +61,6 @@ public class JavaPCAExample {
     for (Vector vector : collectPartitions) {
       System.out.println("\t" + vector);
     }
+    sc.stop();
   }
 }

examples/src/main/scala/org/apache/spark/examples/mllib/AssociationRulesExample.scala

@@ -47,6 +47,8 @@ object AssociationRulesExample {
         + rule.consequent.mkString(",") + "]," + rule.confidence)
     }
     // $example off$
+
+    sc.stop()
   }
 
 }

examples/src/main/scala/org/apache/spark/examples/mllib/BinaryClassificationMetricsExample.scala

@@ -98,6 +98,7 @@ object BinaryClassificationMetricsExample {
     val auROC = metrics.areaUnderROC
     println("Area under ROC = " + auROC)
     // $example off$
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeClassificationExample.scala

@@ -62,6 +62,8 @@ object DecisionTreeClassificationExample {
     model.save(sc, "target/tmp/myDecisionTreeClassificationModel")
     val sameModel = DecisionTreeModel.load(sc, "target/tmp/myDecisionTreeClassificationModel")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/DecisionTreeRegressionExample.scala

@@ -61,6 +61,8 @@ object DecisionTreeRegressionExample {
     model.save(sc, "target/tmp/myDecisionTreeRegressionModel")
     val sameModel = DecisionTreeModel.load(sc, "target/tmp/myDecisionTreeRegressionModel")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/GradientBoostingClassificationExample.scala

@@ -62,6 +62,8 @@ object GradientBoostingClassificationExample {
     val sameModel = GradientBoostedTreesModel.load(sc,
       "target/tmp/myGradientBoostingClassificationModel")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/GradientBoostingRegressionExample.scala

@@ -61,6 +61,8 @@ object GradientBoostingRegressionExample {
     val sameModel = GradientBoostedTreesModel.load(sc,
       "target/tmp/myGradientBoostingRegressionModel")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/IsotonicRegressionExample.scala

@@ -62,6 +62,8 @@ object IsotonicRegressionExample {
     model.save(sc, "target/tmp/myIsotonicRegressionModel")
     val sameModel = IsotonicRegressionModel.load(sc, "target/tmp/myIsotonicRegressionModel")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/LBFGSExample.scala

@@ -84,6 +84,8 @@ object LBFGSExample {
     loss.foreach(println)
     println("Area under ROC = " + auROC)
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/MultiLabelMetricsExample.scala

@@ -64,6 +64,8 @@ object MultiLabelMetricsExample {
     // Subset accuracy
     println(s"Subset accuracy = ${metrics.subsetAccuracy}")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/MulticlassMetricsExample.scala

@@ -90,6 +90,8 @@ object MulticlassMetricsExample {
     println(s"Weighted F1 score: ${metrics.weightedFMeasure}")
     println(s"Weighted false positive rate: ${metrics.weightedFalsePositiveRate}")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/NaiveBayesExample.scala

@@ -45,6 +45,8 @@ object NaiveBayesExample {
     model.save(sc, "target/tmp/myNaiveBayesModel")
     val sameModel = NaiveBayesModel.load(sc, "target/tmp/myNaiveBayesModel")
     // $example off$
+
+    sc.stop()
   }
 }
 

examples/src/main/scala/org/apache/spark/examples/mllib/PCAOnRowMatrixExample.scala

@@ -53,6 +53,8 @@ object PCAOnRowMatrixExample {
     val collect = projected.rows.collect()
     println("Projected Row Matrix of principal component:")
     collect.foreach { vector => println(vector) }
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/PCAOnSourceVectorExample.scala

@@ -52,6 +52,8 @@ object PCAOnSourceVectorExample {
     val collect = projected.collect()
     println("Projected vector of principal component:")
     collect.foreach { vector => println(vector) }
+
+    sc.stop()
   }
 }
 // scalastyle:on println

examples/src/main/scala/org/apache/spark/examples/mllib/PrefixSpanExample.scala

@@ -46,6 +46,8 @@ object PrefixSpanExample {
           ", " + freqSequence.freq)
     }
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:off println

examples/src/main/scala/org/apache/spark/examples/mllib/RandomForestClassificationExample.scala

@@ -62,6 +62,8 @@ object RandomForestClassificationExample {
     model.save(sc, "target/tmp/myRandomForestClassificationModel")
     val sameModel = RandomForestModel.load(sc, "target/tmp/myRandomForestClassificationModel")
     // $example off$
+
+    sc.stop()
   }
 }
 // scalastyle:on println