The hosting services registry was not ported to

djblets.registries.Registry as cleanly as it should have been. As a

result, the "Add repository" form broke, due to missing information on

hosting services. In addition, Review Board 2.0.x introduced a

hosting_service_id attribute which mirrored the id attribute that

3.0.x introduced. We now only use the hosting_service_id attribute.
The "Add repository" form now works correctly and no more errors are

triggered in the log.

Ran unit tests.
Successfully added a repository in the "Add repository" form.