Fix up test data in draft editing feature
Fix up test data in draft editing feature

- make test data more specific to the scenario where it's needed
- use FactoryGirl instead of Payloads
- rename local variables for clarity

alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher