mvn-sync: Possible race condition if artifact changes while being processed

[Aklakan]

Redeploying an artifact with mvn install (or mvn deploy) while the sync job is still running may cause a race condition.
We need to ensure that reprocessing of artifacts that are currently work on gets delayed properly.

In practice, this should be a minor issue but its worth noting it. There might be abuse potential by destructive agents.