Fix logins not published
This addresses a regression from https://lab.nexedi.com/nexedi/erp5/merge_requests/1561 changing the class hierarchy caused Login to loose its docstring and became no longer publishable.
This was problematic because it was not detected by the test suite, so HTML test is changed to use zope publication instead of calling the view on the context.
Another notable point is that this behaves differently in ERP5JS, the Logins were still visible in ERP5JS. Because we don't actually rely on "no docstring on the class" to prevent publication, this is not changed.