When I test emper with a custom kernel in qemu `Runtime::getDefaultWorkerCount()` returns the number of CPU available to the host not the guest running in qemu. But running `nproc(1)` in the guest reports the correct value. That lead me to [the corutils nproc source code](https://github.com/coreutils/gnulib/blob/90e79512d8b385801218d6e9c4d88ff77186560b/lib/nproc.c#L206) they use `min(configured-cpus, online-cpus, cpus-available-to-process)`. We should use something similar.