We were doing all kinds of code gymnastics to "enable" Crowd in the
feature spec and this would sometimes cause a transient failure.
Really what it's testing is if the Crowd login form shows when Crowd's
enabled, so this is much better suited to a view spec.
There is no Kerberos auth in gitlab-ce, so it shouldn't be noted
as a form-driven auth mechanism in app/helpers/auth_helper.rb.
This breaks using Kerberos as a custom omniauth provider.
See issue #2510
