The default `_NPROCESSORS_ONLN` heuristic we have isn't cgroups aware.
So it thinks it has e.g. 40 CPUs when running in a k8s pod. This can
then blow through our allocated resource limits.
Declare some modest amount of RAM and CPU resources and override `make`
parallelism.
This matches what rpm-ostree now does in
https://github.com/coreos/rpm-ostree/pull/2155.