Added clear property to JavaAPISuite to remove port binding errors.

core/src/test/scala/spark/JavaAPISuite.java

@@ -44,6 +44,8 @@ public class JavaAPISuite implements Serializable {
   public void tearDown() {
     sc.stop();
     sc = null;
+    // To avoid Akka rebinding to the same port, since it doesn't unbind immediately on shutdown
+    System.clearProperty("spark.master.port");
   }
 
   static class ReverseIntComparator implements Comparator<Integer>, Serializable {