add kvstore stats
add kvstore stats

Change-Id: I94e04f488562bda759ade2f0a03d5d0604ba87a9
Reviewed-on: http://review.couchbase.org/c/perfrunner/+/156056
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Korrigan Clark <11cf3ebdc6cba78053c91b2fd94cb21b47d0d02e@couchbase.com>

couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner