remove java compiler warnings from java tests

Author: jendap

core/src/test/java/org/apache/spark/JavaAPISuite.java

@@ -63,6 +63,7 @@
 // The test suite itself is Serializable so that anonymous Function implementations can be
 // serialized, as an alternative to converting these anonymous classes to static inner classes;
 // see http://stackoverflow.com/questions/758570/.
+@SuppressWarnings("serial")
 public class JavaAPISuite implements Serializable {
   private transient JavaSparkContext sc;
   private transient File tempDir;

core/src/test/java/org/apache/spark/JavaJdbcRDDSuite.java

@@ -34,6 +34,7 @@
 import org.junit.Before;
 import org.junit.Test;
 
+@SuppressWarnings("serial")
 public class JavaJdbcRDDSuite implements Serializable {
   private transient JavaSparkContext sc;