HWLOC_XMLFILE is lower-level than PRTE_MCA_hwloc_use_topo_file.
Setting PRTE_MCA_hwloc_use_topo_file require processes managed by prterun/mpiexec.
While setting HWLOC_XMLFILE will always work in sandbox environment.
This commit fix the annoying error message
"[hwloc/linux] failed to find sysfs cpu topology directory, aborting linux discovery."
When running mpi4py related python tests not managed by mpiexec.
We are migrating packages that meet below requirements:
1. using `callPackage`
2. called path is a directory
3. overriding set is empty (`{ }`)
4. not containing path expressions other than relative path (to
makenixpkgs-vet happy)
5. not referenced by nix files outside of the directory, other
than`pkgs/top-level/all-packages.nix`
6. not referencing nix files outside of the directory
7. not referencing `default.nix` (since it's changed to `package.nix`)
8. `outPath` doesn't change after migration
The tool is here: https://github.com/Aleksanaa/by-name-migrate.
