ENYO-2514: Add a button to Wait pop-up to cancel a build request.

Link to the JIRA ticket: https://enyojs.atlassian.net/browse/ENYO-2514

Ready for review.

Tested on Chrome, FireFox, (Windows 7)
Enyo-DCO-1.1-Signed-off-by: Rafik Adiche mahmoud-rafik.adiche@hp.com