Fix producer metric reporting non-published version

[AlexandruGhergut]

On each cycle that is run, a toVersion is computed.
The currentVersion metric of the producer is updated on each cycle to the above version. I find that misleading because when there is NO state change, there will be no new version published but the metric will still be updated, pointing to a non-existent version.

If I understood correctly, the producer's readState will be null when there is no state change so I removed the else branch in which the version update happened.

Also added a gradle setting to build the subprojects in parallel.

Use-case for this metric: we want to add an alert for consumers that are out-of-sync with the producer for a given amount of time. For that we look at the consumer's reported version and at the producer's version.

[AlexandruGhergut]

ping @toolbear @rpalcolea @akhaku

[AlexandruGhergut]

Closing this in favor of #459