Introduce method to write msg and get response through OpenFlow.

Change-Id: Ibc92985a98a3b9a178e474f55c117e08b05a8d44
diff --git a/protocols/openflow/api/src/test/java/org/onosproject/openflow/controller/OpenflowControllerAdapter.java b/protocols/openflow/api/src/test/java/org/onosproject/openflow/controller/OpenflowControllerAdapter.java
index 20e2aed..26122e3 100644
--- a/protocols/openflow/api/src/test/java/org/onosproject/openflow/controller/OpenflowControllerAdapter.java
+++ b/protocols/openflow/api/src/test/java/org/onosproject/openflow/controller/OpenflowControllerAdapter.java
@@ -17,6 +17,8 @@
 
 import org.projectfloodlight.openflow.protocol.OFMessage;
 
+import java.util.concurrent.CompletableFuture;
+
 /**
  * Test adapter for the OpenFlow controller interface.
  */
@@ -82,6 +84,11 @@
     }
 
     @Override
+    public CompletableFuture<OFMessage> writeResponse(Dpid dpid, OFMessage msg) {
+        return null;
+    }
+
+    @Override
     public void processPacket(Dpid dpid, OFMessage msg) {
     }