CBQE-0: add GROUP=DELTA in py-failover.conf

Change-Id: Ib34d55b83811ffd78b061fd102b2a00af3531e72
Reviewed-on: http://review.couchbase.org/37652
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>