Introduce NodeJS codegen for Google Cloud Functions. (#4406)

* Another approach: extending NodeJS server to support GCF.

This does not add a new language, but adding some client options
to support Google Cloud Functions (GCF).

* Add URLs for how to deploy the generated code.

Adds the client options help message and the README.md file.

samples/server/petstore/nodejs-google-cloud-functions/controllers/Store.js

@@ -0,0 +1,23 @@
+'use strict';
+
+var url = require('url');
+
+
+var Store = require('./StoreService');
+
+
+module.exports.deleteOrder = function deleteOrder (req, res, next) {
+  Store.deleteOrder(req.swagger.params, res, next);
+};
+
+module.exports.getInventory = function getInventory (req, res, next) {
+  Store.getInventory(req.swagger.params, res, next);
+};
+
+module.exports.getOrderById = function getOrderById (req, res, next) {
+  Store.getOrderById(req.swagger.params, res, next);
+};
+
+module.exports.placeOrder = function placeOrder (req, res, next) {
+  Store.placeOrder(req.swagger.params, res, next);
+};