[ONOS-7902] Add default implementation of k8s node with unit tests

Change-Id: I283967ae14dc7f38e749d7407e4bec698536c18b
diff --git a/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sNode.java b/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sNode.java
index 8f307b5..13b1f47 100644
--- a/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sNode.java
+++ b/apps/k8s-node/api/src/main/java/org/onosproject/k8snode/api/K8sNode.java
@@ -89,6 +89,14 @@
     K8sNodeState state();
 
     /**
+     * Returns new kubernetes node instance with given state.
+     *
+     * @param newState updated state
+     * @return updated kubernetes node
+     */
+    K8sNode updateState(K8sNodeState newState);
+
+    /**
      * Returns the GRE tunnel port number.
      *
      * @return GRE port number; null if the GRE tunnel port does not exist