Allow built in Observatory to work on any port

runtime/bin/vmservice/client/lib/src/app/application.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of app;
 
 /// A request response interceptor is called for each response.
 typedef void RequestResponseInterceptor();
 
 /// The observatory application. Instances of this are created and owned
@@ skipping 18 matching lines @@
   }
 
   ObservatoryApplication.devtools() :
       locationManager = new LocationManager(),
       vm = new DartiumVM() {
     _initOnce();
   }
 
   ObservatoryApplication() :
       locationManager = new LocationManager(),
-      vm = new HttpVM('http://127.0.0.1:8181/') {
+      vm = new HttpVM() {
     _initOnce();
   }
 }