Change the matcher on 'message' to require exact matches [#72627064]

- Previously we've been doing a regex match that didn't need to match the message field exactly
- This meant changes to error messages were only being partially matched/partially tested
Pass back data-set name to write and create api methods [#72627064]
Fix tests [#72627064]

- Tests now expect the presence of a data-set name
Add in a specific test for parse errors

- Different environments (e.g. Travis) will throw different types of parse error, so having an exact match isn't desirable/going to pass.
- However, we don't want to lose the exact matchers on other messages, as they are useful tests
Merge pull request #312 from alphagov/add_dataset_name_to_error_messages

Add dataset name to error messages [#72627064]