[#736] Closing of Vert.x instance should be waited on

Author: Sanne

hibernate-reactive-core/src/main/java/org/hibernate/reactive/vertx/impl/DefaultVertxInstance.java

@@ -34,7 +34,7 @@ public Vertx getVertx() {
     @Override
     public void stop() {
         if ( vertx != null ) {
-            vertx.close();
+            vertx.close().toCompletionStage().toCompletableFuture().join();
         }
     }