Fix: double check resource existence at receiving addition event

Change-Id: I80fb2b30201e3e770eb5384ecee2b78b32502936
diff --git a/apps/k8s-networking/app/src/main/java/org/onosproject/k8snetworking/impl/K8sNetworkPolicyWatcher.java b/apps/k8s-networking/app/src/main/java/org/onosproject/k8snetworking/impl/K8sNetworkPolicyWatcher.java
index 311ac8a..3ded560 100644
--- a/apps/k8s-networking/app/src/main/java/org/onosproject/k8snetworking/impl/K8sNetworkPolicyWatcher.java
+++ b/apps/k8s-networking/app/src/main/java/org/onosproject/k8snetworking/impl/K8sNetworkPolicyWatcher.java
@@ -172,7 +172,10 @@
             log.trace("Process network policy {} creating event from API server.",
                     networkPolicy.getMetadata().getName());
 
-            k8sNetworkPolicyAdminService.createNetworkPolicy(networkPolicy);
+            if (k8sNetworkPolicyAdminService.networkPolicy(
+                    networkPolicy.getMetadata().getUid()) == null) {
+                k8sNetworkPolicyAdminService.createNetworkPolicy(networkPolicy);
+            }
         }
 
         private void processModification(NetworkPolicy networkPolicy) {