Add vbucket-details stats to the stats.org file

Change-Id: I558713c554e3e9e4932597e9e7b8966ddb450bf8
Reviewed-on: http://review.couchbase.org/39701
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>