CBQE-1718: fix rebalance out code in upgrade xdcr tests

Change-Id: I46bf4b3a1b23ec48183ee407887f7daed1b23bc0
Reviewed-on: http://review.couchbase.org/30753
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>