Update republishing task logic
Update republishing task logic

To:
- Return the content_id of the item that hasn't been published correctly

- Do not stop the rake task when an item cannot be published Terminating the task
does not mean the that the publishing of the items published before the
unpublishable item is going to be undone.  These changes make that the rake
task continues publishing all the tags even if some of them cannot be published
for some reason.

alphagov/collections-publisher,alphagov/collections-publisher,alphagov/collections-publisher