I like it this way, because it's a good test case for `_init_keys`. I'm catching both exposure and offset which are handed off to super base.Model and for loglike_method that needs to be added in the class.

I don't see a reason to replace this with several special cases that would have to be removed again in the next PR.
I can add a `link_test` to this PR (or in the next) where I need exactly the same generic code or lot's of special cases:  https://github.com/statsmodels/statsmodels/issues/1479#issuecomment-37724805