[Onyxia] Allow shamans to queue rdf as tanks

Horde is really low on tanks. Cuz we don't have paladins, it's just unfair to not let us tank as shamans. Ye, shaman tank is not the best choice but it's not worse than paladin tank. And it's much better than 1h+ in rdf queue.
Everyone knows it works. Everyone knows it's not super good. But it's works. Right now I can't even queue with preformed group where everyone fine with shaman tank. So please let as tank. At least let's try it in the test mode for a week or two and see how it works. You always can disable it