fix: (vNet) class load issues for OSGi bundle.

Problem.
1. Inside incubator package, class loader can't search classes defined
   in the other bundles such as onos-core

Solution
1. Added a method to return bundle context, and obtain class loader.

Change-Id: If5ee4cb1a5b9ef5ab7d7e3bbc70408ea8257baea
diff --git a/incubator/api/src/test/java/org/onosproject/incubator/net/virtual/event/AbstractVirtualListenerManagerTest.java b/incubator/api/src/test/java/org/onosproject/incubator/net/virtual/event/AbstractVirtualListenerManagerTest.java
index 23934b5..6614941 100644
--- a/incubator/api/src/test/java/org/onosproject/incubator/net/virtual/event/AbstractVirtualListenerManagerTest.java
+++ b/incubator/api/src/test/java/org/onosproject/incubator/net/virtual/event/AbstractVirtualListenerManagerTest.java
@@ -38,6 +38,7 @@
 import org.onosproject.incubator.net.virtual.VirtualNetworkService;
 import org.onosproject.incubator.net.virtual.VirtualPort;
 import org.onosproject.net.DeviceId;
+import org.osgi.framework.BundleContext;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -52,24 +53,22 @@
  */
 public class AbstractVirtualListenerManagerTest {
 
-    private VirtualNetworkService manager;
-
-    TestEventDispatcher dispatcher = new TestEventDispatcher();
-    VirtualListenerRegistryManager listenerRegistryManager =
+    private TestEventDispatcher dispatcher = new TestEventDispatcher();
+    private VirtualListenerRegistryManager listenerRegistryManager =
             VirtualListenerRegistryManager.getInstance();
 
-    PrickleManager prickleManager;
-    PrickleListener prickleListener;
+    private PrickleManager prickleManager;
+    private PrickleListener prickleListener;
 
-    GooManager gooManager;
-    GooListener gooListener;
+    private GooManager gooManager;
+    private GooListener gooListener;
 
-    BarManager barManager;
-    BarListener barListener;
+    private BarManager barManager;
+    private BarListener barListener;
 
     @Before
     public void setUp() {
-        manager = new TestVirtualNetworkManager();
+        VirtualNetworkService manager = new TestVirtualNetworkManager();
 
         dispatcher.addSink(VirtualEvent.class, listenerRegistryManager);
 
@@ -153,25 +152,25 @@
     private enum Type { FOO }
 
     private static class Thing extends AbstractEvent<Type, String> {
-        protected Thing(String subject) {
+        private Thing(String subject) {
             super(Type.FOO, subject);
         }
     }
 
     private static class Prickle extends Thing {
-        protected Prickle(String subject) {
+        private Prickle(String subject) {
             super(subject);
         }
     }
 
     private static class Goo extends Thing {
-        protected Goo(String subject) {
+        private Goo(String subject) {
             super(subject);
         }
     }
 
     private static class Bar extends Thing {
-        protected Bar(String subject) {
+        private Bar(String subject) {
             super(subject);
         }
     }
@@ -198,19 +197,19 @@
 
     private class PrickleManager extends AbstractVirtualListenerManager<Prickle, PrickleListener> {
         public PrickleManager(VirtualNetworkService service, NetworkId networkId) {
-            super(service, networkId);
+            super(service, networkId, Prickle.class);
         }
     }
 
     private class GooManager extends AbstractVirtualListenerManager<Goo, GooListener> {
         public GooManager(VirtualNetworkService service, NetworkId networkId) {
-            super(service, networkId);
+            super(service, networkId, Goo.class);
         }
     }
 
     private class BarManager extends AbstractVirtualListenerManager<Bar, BarListener> {
         public BarManager(VirtualNetworkService service, NetworkId networkId) {
-            super(service, networkId);
+            super(service, networkId, Bar.class);
         }
     }