Test running tasks in create-traballs.sh script in parallel, 4 at a time

I am running at test on colchicifolium where I execute task in the create-tarballs script in parallel, 4 at a time.

I am testing how much time we can save with the overall execution and if we will use give or take the same resources (monitoring: https://grafana1.torproject.org/d/Z7T7Cfemz/node-exporter-full?orgId=1&var-job=node&var-node=colchicifolium.torproject.org&var-port=9100)

@lavamind @anarcat please let me know what you think.