This method was duplicating dataset has_one :certificate behaviour
Raise not found if dataset is not found
Return 404 on unpublished certificate
This is not the correct place to test for this behaviour

It should be enforced at the model level, as the state this test
sets up is not reproducable in the normal operation of the system.
Merge pull request #993 from theodi/bugfix-404-on-not-finding-dataset-for-url

404 on unfound datasets lookup by url