Zookeeper supports a number of "4 letter" commands [0] which are useful
for debugging and general diagnostics. By default only srvr is enabled,
but we want to add stat and dump to see details on server and client
connection statuses.
We do this via the 4lw.commands.whitelist configuration option [1] and
not the docker image env vars because we're mounting a zoo.cfg in
already.
[0] https://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_4lw
[1] https://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_clusterOptions
Change-Id: I24ea9b37cd5766c9d393106e8eab34623cad1624
3f2dd0e681