CBQE-1003: skip cleanup for failed xdcr upgrade tests

Change-Id: Ie5349998a7968a13218e4905af3cbdfb4dfddd3d
Reviewed-on: http://review.couchbase.org/25036
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>