RepositoryForm always fed in any submitted data to each repository and

bug tracker form, with the idea being that those forms would ignore any

data they didn't care about. This assumption was no longer valid with

the addition of Gerrit, which assumed the existence of a field in the

data, breaking all hosting services except for Gerrit.
This bad assumption is also what would lead to validation errors

appearing if submitting a form with bad/missing data and then switching

hosting services or plans. Those previously-hidden forms would appear,

showing that the fields were required.
We now only bind data to a form if the form in question is the one we're

posting to.

Manually tested with and without hosting services, and with different

setups for plans. Triggered validation errors and then went around other

forms to make sure that other forms hadn't validated.
I was also able to successfully submit without the gerrit_url error.
Unit tests pass.