Fix: to register eventlisteners for virtualnetwork

Changes.
1. Virtual network service inherite listener service

Change-Id: Ie2911916b2912e3c8cbd2069e9563e1f5e2c837f
diff --git a/incubator/net/src/test/java/org/onosproject/incubator/net/virtual/impl/provider/DefaultVirtualFlowRuleProviderTest.java b/incubator/net/src/test/java/org/onosproject/incubator/net/virtual/impl/provider/DefaultVirtualFlowRuleProviderTest.java
index d8ae05d..0d3c8cc 100644
--- a/incubator/net/src/test/java/org/onosproject/incubator/net/virtual/impl/provider/DefaultVirtualFlowRuleProviderTest.java
+++ b/incubator/net/src/test/java/org/onosproject/incubator/net/virtual/impl/provider/DefaultVirtualFlowRuleProviderTest.java
@@ -39,6 +39,7 @@
 import org.onosproject.incubator.net.virtual.VirtualLink;
 import org.onosproject.incubator.net.virtual.VirtualNetwork;
 import org.onosproject.incubator.net.virtual.VirtualNetworkAdminService;
+import org.onosproject.incubator.net.virtual.VirtualNetworkListener;
 import org.onosproject.incubator.net.virtual.VirtualPort;
 import org.onosproject.net.ConnectPoint;
 import org.onosproject.net.DefaultAnnotations;
@@ -452,6 +453,16 @@
                                       PortNumber portNumber) {
 
         }
+
+        @Override
+        public void addListener(VirtualNetworkListener listener) {
+
+        }
+
+        @Override
+        public void removeListener(VirtualNetworkListener listener) {
+
+        }
     }
 
     private static class TestTopologyService extends TopologyServiceAdapter {