Expose running current tests on /builds site.

Currently, only enabled for canary but can be enabled for beta once
1.9.0-beta.2 is released.

![screenshot](http://monosnap.com/image/YWX2rk5Zg8357KKnJaUJo1A5moBIrd.png)

Links to http://builds.emberjs.com/canary/ember-tests-index.html which allows running Ember's full test suite.