AGJS-239 Promisfy Authorization

https://issues.jboss.org/browse/AGJS-239

* replaced jQuery.mockjax with Sinon.fakeServer

To be applied after https://github.com/aerogear/aerogear-js/pull/146
this value isn't actually in the responseText field,  will be returned in "xhr.response"

i'm preparing a PR for this