Add manifest build to groups portal release job

Generate a manifest file during groups portal release job
to enlist the available development and production release
information for third party Drupal deployment tools like drush.
The manifest file will be published under
http://tarballs.openstack.org/groups/drupal-updates/release-history/groups/7.x
url.

Change-Id: I48f694cbc2ea46d41a10aafb8b51ebb0a50f7ef4
Merge "Add manifest build to groups portal release job"