CBQE-1158: Automation tests- Optimistc XDCR

- Set XDCR_LATENCY_OPTMIZATION to true

Change-Id: Ie099a35bd20a185845ededa370da47d1ec210ce8
Reviewed-on: http://review.couchbase.org/25296
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: abhinav dangeti <abhinav.dangeti@gmail.com>