Add metaData option for .visit

Allows an option of metaData to be passed into options like:
  fastboot.visit('', { metaData: { foo: 'bar' } });

This enables per request information to be passed into the app such
as user session info.

Author: thoov

src/ember-app.js

@@ -199,7 +199,11 @@ class EmberApp {
     let html = options.html || this.html;
 
     let bootOptions = buildBootOptions();
-    let fastbootInfo = new FastBootInfo(req, res, this.hostWhitelist);
+    let fastbootInfo = new FastBootInfo(
+      req,
+      res,
+      { hostWhitelist: this.hostWhitelist, metaData: options.metaData }
+    );
     let doc = bootOptions.document;
 
     let instance;

src/fastboot-info.js

@@ -7,13 +7,16 @@ var FastBootResponse = require('./fastboot-response');
  * current HTTP request from FastBoot. This is injected
  * on to the FastBoot service.
  */
-function FastBootInfo(request, response, hostWhitelist) {
+function FastBootInfo(request, response, options = {}) {
+  const { hostWhitelist, metaData } = options;
+
   this.deferredPromise = RSVP.resolve();
   if (request) {
     this.request = new FastBootRequest(request, hostWhitelist);
   }
 
   this.response = new FastBootResponse(response || {});
+  this.metaData = metaData;
 }
 
 FastBootInfo.prototype.deferRendering = function(promise) {