Remove ReadStream methods with callbacks and propagate in the stack

Author: vietj

src/main/java/io/vertx/httpproxy/impl/ProxiedResponse.java

@@ -229,7 +229,7 @@ public void send(Handler<AsyncResult<Void>> completionHandler) {
         // Special handling for HTTP 1.0 clients that cannot handle chunked encoding
         // we need to buffer the content
         BufferingWriteStream buffer = new BufferingWriteStream();
-        body.stream().pipeTo(buffer, ar -> {
+        body.stream().pipeTo(buffer).onComplete(ar -> {
           if (ar.succeeded()) {
             Buffer content = buffer.content();
             proxiedResponse.end(content).onComplete(completionHandler);