Code quality requires `codequality.json` to be the only artifact file in the job

There seems to be a limitation on the codequality.json (or codeclimate.json) parsing where it needs to be the only artifact file for the job. For example if you try to also persist the HTML report, errors can occur. (See https://gitlab.com/gitlab-org/gitlab-ee/issues/2871).

We should support multiple files in the report, as people may want to output the HTML to a Pages server, for example.