Keys based on longs should display in hexadecimal

Change-Id: I45d826a4e8c24271d6689f9438d5eca78f557241

@@ -103,7 +103,7 @@ public class Key {
 
         @Override
         public String toString() {
-            return Long.toString(key);
+            return "0x" + Long.toHexString(key);
         }
 
         @Override

@@ -56,7 +56,6 @@ import static org.onosproject.net.NetTestTools.link;
 /**
  * Tests for the objective tracker.
  */
-@Ignore
 public class ObjectiveTrackerTest {
     private static final int WAIT_TIMEOUT_SECONDS = 2;
     private Topology topology;