Increase timeout of qunit

On busy system chrome may take more than 30000ms to answer.
(grafted from 45edcc428aef14cb81475bda31190b7baa984840)

--HG--
branch : 6.0

Gruntfile.js

@@ -135,6 +135,7 @@ module.exports = function(grunt) {
     },
     qunit: {
         options: {
+            timeout: 300000,
             puppeteer: {
                 headless: true,
                 args: [