CBQE-1003: initial xdcr upgrade tests

Change-Id: Iff5e8282271555d6012e9ccc953b554f8d7fbe89
Reviewed-on: http://review.couchbase.org/24323
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>