b5a328e58f
Since #104094 (d22b3ed4bc), NixOS is
using the unified cgroup hierarchy by default (aka cgroupv2).
This means the blkio controller isn't there, so we should test for
something else (e.g. the presence of the io controller).
Fixes #105581.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at https://nixos.org/nixos and in the manual in doc/manual.