[SPARK-12376][TESTS] Spark Streaming Java8APISuite fails in assertOrderInvariantEquals method

org.apache.spark.streaming.Java8APISuite.java is failing due to trying to sort immutable list in assertOrderInvariantEquals method.

Author: Evan Chen <chene@us.ibm.com>

Closes #10336 from evanyc15/SPARK-12376-StreamingJavaAPISuite.

extras/java8-tests/src/test/java/org/apache/spark/streaming/Java8APISuite.java

@@ -439,9 +439,14 @@ public class Java8APISuite extends LocalJavaStreamingContext implements Serializ
    */
   public static <T extends Comparable<T>> void assertOrderInvariantEquals(
     List<List<T>> expected, List<List<T>> actual) {
-    expected.forEach((List<T> list) -> Collections.sort(list));
-    actual.forEach((List<T> list) -> Collections.sort(list));
-    Assert.assertEquals(expected, actual);
+    expected.forEach(list -> Collections.sort(list));
+    List<List<T>> sortedActual = new ArrayList<>();
+    actual.forEach(list -> {
+        List<T> sortedList = new ArrayList<>(list);
+        Collections.sort(sortedList);
+        sortedActual.add(sortedList);
+    });
+    Assert.assertEquals(expected, sortedActual);
   }
 
   @Test