Fixes #6182 - Dynflowized repository update

- [x] Dynflowize repository update
- [x] Fix old tests
- [x] Make new tests
Looks like the vendor field gets set no matter what - https://github.com/Katello/katello/blob/master/app/lib/actions/candlepin/product/content_update.rb#L34 -- although I'd argue that it probably makes more sense to set it to the repository.product.provider type but in the end I don't think it really matters.