Updating subscription should use node version

[chemicL]

When a user updates a newly created subscription, the state update might be lost due to overwriting behaviour in ZookeeperBasedRepository.

The overwrite operation users should include a call to get the version of the data and repeat in a CAS like manner.

In the case I observed a consumer was just created for the subscription and the ACTIVE state got set, but in the meantime a subscription update event has happened and lost that state transition.