testing: create test matrix for cpuset partitioning

[shoenig]

Nomad 1.7 is reworking how cgroups and especially the cpuset controller are managed. Existing unit tests don't do a great job of ensuring things work as expected. Ideally we would have a test matrix that explicitly covers every permutation of

drivers: raw_exec, exec, docker, podman
cgroups version: v1, v2
resource: cpu, cores, mixed

This would probably be a separate CI workflow so we can make use of older ubuntu-20.04 runners which are configured with cgroups v1.

Similar to API tests I'd want to launch a real Nomad agent rather than fabricating the "driver harness" used in driver/ tests currently. The harness makes a lot of false assumptions about what the real client would actually be doing.