ONOS-1326: Added support for observing when node liveness status was last updated. Useful for detecting/debugging stability issues.

Change-Id: I8ffebcf3a09a51c6e3e7526986a0f05530ed757f
diff --git a/core/api/src/test/java/org/onosproject/cluster/ClusterServiceAdapter.java b/core/api/src/test/java/org/onosproject/cluster/ClusterServiceAdapter.java
index 35b5a6d..5afaec6 100644
--- a/core/api/src/test/java/org/onosproject/cluster/ClusterServiceAdapter.java
+++ b/core/api/src/test/java/org/onosproject/cluster/ClusterServiceAdapter.java
@@ -17,6 +17,8 @@
 
 import java.util.Set;
 
+import org.joda.time.DateTime;
+
 /**
  * Test adapter for the cluster service.
  */
@@ -42,6 +44,11 @@
     }
 
     @Override
+    public DateTime getLastUpdated(NodeId nodeId) {
+        return null;
+    }
+
+    @Override
     public void addListener(ClusterEventListener listener) {
     }