this class is used to clean up the
snapshot and data log dir's. This is usually
run as a cronjob on the zookeeper server machine.
Invocation of this class will clean up the datalogdir
files and snapdir files keeping the last "-n" snapshot files
and the corresponding logs.
Purges the snapshot and logs keeping the last num snapshots and the
corresponding logs. If logs are rolling or a new snapshot is created
during this process, these newest N snapshots or any data logs will be
excluded from current purging cycle.