Attempt to fix sporadic NettyMessagingManagerTest failure.

Change-Id: Iae570c329a3fe0e7e46f9caf13a5b283a2153ed4
diff --git a/core/store/dist/src/main/java/org/onosproject/store/cluster/messaging/impl/NettyMessagingManager.java b/core/store/dist/src/main/java/org/onosproject/store/cluster/messaging/impl/NettyMessagingManager.java
index aefea6c..4f303a5 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/cluster/messaging/impl/NettyMessagingManager.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/cluster/messaging/impl/NettyMessagingManager.java
@@ -280,7 +280,7 @@
             if (e != null) {
                 callbacks.invalidate(messageId);
             }
-        }).thenCompose(v -> response);
+        }).thenComposeAsync(v -> response, executor);
     }
 
     @Override