Promoting WikiGrok to stable and disabling for anons (with flag)

See:
https://trello.com/c/oE0pz4EK/5-5-wikigrok-a-b-test-in-stable-logged-in

Change-Id: Id0b1bdc26636c51abb405566eb1a5a39346fe10b
(cherry picked from commit Id0b1bdc26636c51abb405566eb1a5a39346fe10b)