zookeeper runs under coreos fleet control
because issue:ZOOKEEPER-1506, I have to use the snapshot version
sidekick using systemd bug: 89087
the workaround (maybe it is the correct way) is to set the sidekick unit in the main uint's
otherwise if the main unit is stop and start again, the sidekick will not be restarted.
note: don't use the Requires in the systemd unit. otherwise it will not restart when required units failed