Stat the realtime tps of zookeepr server


Apache issue: ZOOKEEPER-1804(https://issues.apache.org/jira/browse/ZOOKEEPER-1804)

If you also want to know how client use zookeeper, and the real time r/w ps of each zookeeper client, you can use the patch "ZOOKEEPER-1804-2.patch"
use java properties: -Dserver_process_stats=true to open the function.
Sample:
$>echo rwps|nc localhost 2181
RealTime R/W Statistics:
getChildren2:　　　0.5994005994005994
createSession:　　1.6983016983016983
closeSession:　　　0.999000999000999
setData:　　　　　110.18981018981019
setWatches:　　　129.17082917082917
getChildren:　　　 68.83116883116884
delete:　　　　　　19.980019980019982
create: 　　　　　 22.27772227772228
exists:　　　　　　1806.2937062937062
getDate:　　　　　729.5704295704296