CircleCI: Ensure correct level of parallelism
CircleCI: Ensure correct level of parallelism

This setting got flipped in CircleCI somehow and caused build failures.

Add a check for it at the very beginning of the build and print an
informative message in case it happens again.

MarcoLotz/docker-client,bgokden/docker-client,mthmulders/docker-client,SerCeMan/docker-client,spotify/docker-client,skinzer/docker-client,rgarbin/docker-client,rgrunber/docker-client,rgarbin/docker-client,davidkarlsen/docker-client,anokun7/docker-client,bgokden/docker-client,nurkiewicz/docker-client,mthmulders/docker-client,davidkarlsen/docker-client,skinzer/docker-client,xcoulon/docker-client,kwart/docker-client,xcoulon/docker-client,MarcoLotz/docker-client,anokun7/docker-client,ravwojdyla/docker-client,ravwojdyla/docker-client,nurkiewicz/docker-client,SerCeMan/docker-client,rgrunber/docker-client,spotify/docker-client,kwart/docker-client