docs: function createExpressAppServer(app, port) {
    return new P(function(resolve, reject) {
      var appServer = app.listen(port, function() {
        var addr = appServer.address();
        resolve({
            app: app,
            appServer: appServer,
            serverUrl: url.format({ protocol: 'http', hostname: addr.address, port: addr.port })
        });
      });
    });
  }