Fix a bad regression with the review group form.
Fix a bad regression with the review group form.

Due to a quirk in the way forms are initialized, the review group form was
losing the "name" and "display name" fields before validation. This caused
saving new items to always fail.

Passing the local_site_name all the way through kwargs fixes the issue. I've
applied the same fix to the `DefaultReviewerForm`, and made both call the
superclass' `clean` method, just for completeness.

Testing done:
Was able to save new review groups and default reviewers.

Reviewed at https://reviews.reviewboard.org/r/8430/

sgallagher/reviewboard,brennie/reviewboard,chipx86/reviewboard,brennie/reviewboard,reviewboard/reviewboard,davidt/reviewboard,davidt/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,davidt/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,brennie/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,davidt/reviewboard,brennie/reviewboard,chipx86/reviewboard,reviewboard/reviewboard