My job as a "tank" in Rated Battlegrounds has either been to carry the flag or to prevent the other team from capping Waterworks on the Gilneas map. In either case you'll want to maximize your survivability through Resilience, Stamina and talents that hinder the opposing team or help yours. DPS is not something you worry about. All of which assumes that this will be your primary pvp focus.
If it's just something you want to try out and your team isn't hardcore about their ratings, then your regular tank spec will suffice and you can gem/enchant your pvp gear for dps. Resilience will still be very important and you won't want to be in raid gear.
How does a PC gamer change a light bulb? He doesn't. He goes on the forums and QQs about it being dark.