RepositoryForm does a lot of work to build and populate subforms, but

it wasn't complete. While the main RepositoryForm initial data was

populated by way of the parent ModelForm, the relevant subforms never

had their own initial data set, nor did they necessarily have the right

form data set from an existing instance.
This regressed the API. Performing an HTTP PUT on the repository

resource would error out unless name and path were explicitly

provided, since those model-level attributes never transitioned properly

to the subforms. We didn't have suitable test coverage for this, so it

wasn't noticed before
This change updates active subforms for an existing instance to have

their initial data for these model-level fields set properly. It also

improves the test suite just a bit to better catch some of this and to

leverage the built-in tests for PUT requests. More work still needs to

be done to better flesh out these tests, which will be handled in a

separate change.

All unit tests pass.