Don't require clustered to be set when creating a clustered vert.x

src/main/java/io/vertx/core/impl/VertxFactoryImpl.java

@@ -37,13 +37,15 @@ public Vertx vertx() {
   @Override
   public Vertx vertx(VertxOptions options) {
     if (options.isClustered()) {
-      throw new IllegalArgumentException("Please use the asynchronous method to create a clustered Vertx");
+      throw new IllegalArgumentException("Please use Vertx.clusteredVertx() to create a clustered Vert.x instance");
     }
     return new VertxImpl(options);
   }
 
   @Override
   public void clusteredVertx(VertxOptions options, final Handler<AsyncResult<Vertx>> resultHandler) {
+    // We don't require the user to set clustered to true if they use this method
+    options.setClustered(true);
     new VertxImpl(options, resultHandler);
   }
 

src/test/java/io/vertx/test/core/CreateVertxTest.java

@@ -62,14 +62,19 @@ public void testCreateClusteredVertxAsync() {
     await();
   }
 
+  /*
+  If the user doesn't explicitly set clustered to true, it should still create a clustered Vert.x
+   */
   @Test
-  public void testCreateNonClusteredVertxAsync() {
+  public void testCreateClusteredVertxAsyncDontSetClustered() {
     VertxOptions options = new VertxOptions();
     Vertx.clusteredVertx(options, ar -> {
       assertTrue(ar.succeeded());
       assertNotNull(ar.result());
+      assertTrue(options.isClustered());
       testComplete();
     });
     await();
   }
+
 }