Initialize partition owner with consumerId

[ismriv]

This avoids a race condition in checkPartitionOwnership, where another instance may create the node initialized to null, so the node will exist, it will try to get its contents but will fail in the comparison consumerId !== data.toString() since data may be null.

[haio]

Hi, what issue will this pr solve?

[ismriv]

The following error:

TypeError: Cannot call method 'toString' of undefined
    at /activity-processor/node_modules/kafka-node/lib/zookeeper.js:395:53
    at /activity-processor/node_modules/kafka-node/node_modules/node-zookeeper-client/index.js:165:26
    ...

[haio]

how to reproduce this error?

[ismriv]

Having a few instances running, and restarting one of them to trigger the rebalancing mechanism. It's a race condition, so it may be tricky to reproduce, but if you try this a few times it will finally happen.

[ismriv]

Any red flags?

[haio]

Still can't reproduce it, but this a improvement logically, so I think it can be merged.

[ismriv]

Brilliant! Thanks.