Test nullity of fields in tearDown method

Author: adutra

integration-tests/src/test/java/com/datastax/oss/driver/core/PeersV2NodeRefreshIT.java

@@ -45,8 +45,12 @@ public static void setup() {
 
   @AfterClass
   public static void tearDown() {
-    cluster.stop();
-    peersV2Server.close();
+    if (cluster != null) {
+      cluster.stop();
+    }
+    if (peersV2Server != null) {
+      peersV2Server.close();
+    }
   }
 
   @Test