(PDB-574) 404 should be returned when querying for a missing catalog

Previously a schema validation error was being thrown (returning a 500).
Now 404 is returned with an error message indicating it could not find
the catalog.
Merge pull request #918 from senior/ticket/master/pdb-574-404-when-catalog-not-found

(PDB-574) 404 should be returned when querying for a missing catalog