[ONOS-5731] Implement skeleton of VirtualNetworkPacketManager

Changes
1. Added VirtualNetworkPacketManager
2. Added VirtualNetworkPacketStore interface and impl class
3. Added VirtualPacketStore impl
4. Simple test cases are added

Todo
1. More test cases

Change-Id: I86f0484a9ee038dab8716703f0e5e41cbcf30cb1
diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java
index 2e852e8..21f721c 100644
--- a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/VirtualNetworkService.java
@@ -17,6 +17,7 @@
 
 import com.google.common.annotations.Beta;
 import org.onlab.osgi.ServiceDirectory;
+import org.onosproject.core.ApplicationId;
 import org.onosproject.net.DeviceId;
 
 import java.util.Set;
@@ -112,4 +113,12 @@
      * @return a service directory
      */
     ServiceDirectory getServiceDirectory();
+
+    /**
+     * Returns the application identifier for a virtual network.
+     *
+     * @param networkId network identifier
+     * @return an representative application identifier for a virtual network
+     */
+    ApplicationId getVirtualNetworkApplicationId(NetworkId networkId);
 }