Publishing of repository availability in zookeeper should be optional.

[bruno]

Some Lily nodes might be configured to perform a dedicated function, for example only index, only be WAL or MQ processor.

However, when such nodes need to access the repository, it would not make much sense to talk to another Lily node for that. It makes more sense to enable the repository module in such nodes, since this is just a lightweight access layer on top of HBase.

But in such cases the repository module should not register itself in ZK, since we do not want it to be used by other clients.