[PULP-317] Make package layout in the published repository configurable

[dralley]

closes #3874

[pedro-psb]

@dralley rpm_distribution_factory returns a client RpmDistributionResponse (or something like that, you can find all those client request/response classes at pulp-openapi-generator/pulp_rpm-client/ dir.
And all those factory fixtures already creates the resource with the cleanup hook.

So you can call the factory without worryng with the api call/cleanup:

dsitribution = rpm_distribution_factory(publication=publication_href)

obs: pulp_smash factories did generate the body data, but every other I've seen just return the object.