CBQE-1053: wrong list of servers in verify_xdcr_stats

Change-Id: Ic693cdaf6d5a5a4309dac74f8e95a6c2edb89cbb
Reviewed-on: http://review.couchbase.org/24773
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>