code: @Override
    public void deregisterHost(final String host)
        throws HostNotFoundException, HostStillInUseException {
      final ZooKeeperClient client = provider.get("deregisterHost");
      ZooKeeperRegistrarUtil.deregisterHost(client, host);
    }
docs: Undoes the effect of {@link ZooKeeperMasterModel#registerHost(String, String)}.  Cleans up
  any leftover host-related things.