CBQE-926: added test to repro mb-6591

Change-Id: Ib033075070d176d059639c130a54823b270348e4
Reviewed-on: http://review.couchbase.org/23981
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: buildbot <build@couchbase.com>