Unit tests for driver manager and driver registry

src/main/java/net/floodlightcontroller/core/internal/Controller.java

@@ -2135,6 +2135,14 @@ public class Controller implements IFloodlightProviderService,
         }
     }
 
+    /**
+     * FOR TESTING ONLY
+     * check if update queue is empty
+     */
+    boolean isUpdateQueueEmptyForTesting() {
+        return this.updates.isEmpty();
+    }
+
     /**
      * FOR TESTING ONLY
      * @param update