add baseline kv test (for xdcr cpu utilization)

Change-Id: Ie9044b083e9d6832ab0f70499f7b011a755d3368
Reviewed-on: http://review.couchbase.org/38783
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>