Comment 3 for bug 1996612

After some more testing with Takashi++, we found the following:
- 2.14 seems to explode the "serial" limit, and runs everything up to a point it can't do anything
- 2.13 is far more conservative with the amount of running things - especially hosts.

A proposal is to link the "serial" option for the playbook to the amount of CPU, with a way to override it via an option to the container build CLI. At least, this is working fine locally, we'll do some more tests within the CI.