use renderMode from the fastboot schema if available

Author: mansona

packages/fastboot/src/ember-app.js

@@ -40,6 +40,7 @@ class EmberApp {
     this.appName = config.appName;
     this.html = config.html;
     this.sandboxRequire = config.sandboxRequire;
+    this.renderMode = config.renderMode;
 
     if (process.env.APP_CONFIG) {
       let appConfig = JSON.parse(process.env.APP_CONFIG);
@@ -300,7 +301,7 @@ class EmberApp {
     let shouldRender = options.shouldRender !== undefined ? options.shouldRender : true;
     let renderMode = process.env.EXPERIMENTAL_RENDER_MODE_SERIALIZE
       ? 'serialize'
-      : options.renderMode;
+      : options.renderMode || this.renderMode;
     let bootOptions = buildBootOptions(shouldRender, renderMode);
     let fastbootInfo = new FastBootInfo(req, res, {
       hostWhitelist: this.hostWhitelist,