[524] Fixes more tests

The MockDrupal server now shuts down cleanly when asked to, however
some of the ONS tests are broken and as a result teardown isn't being
called on MockDrupalCase and the process not shut down.  Needs closer
investigation but the interface the tests are using seems to have changed.
Merge branch 'master' of github.com:datagovuk/ckanext-dgu