Issue #2666926 by helmo: Add a test to create a custom verify task for the hostmaster site and place it in the queue.

The old version was failing on the download of fullcalendar https://www.drupal.org/node/2333881

The previous .build extension started causing trouble since Drush make became more strict about the filename.

See: https://www.drupal.org/node/2373835#comment-9333915 and https://github.com/drush-ops/drush/issues/983