lxc: controller: Fix container launch on cgroup v1

lxc: controller: Fix container launch on cgroup v1

With cgroup v1 I'm seeing LXC container startup failures:

$ sudo virt-install --connect lxc:/// --name test-container --memory 128
--boot init=/bin/sh

Starting install...
ERROR    error from service:
GDBus.Error:org.freedesktop.machine1.NoMachineForPID: PID 2145047 does
not belong to any known machine

libvirt 7.0.0 works but 7.1.0+ does not. The root error seems to predate
that, showing up in syslog, but commit 9c1693eff made it fatal:

commit 9c1693eff427661616ce1bd2795688f87288a412
Author: Pavel Hrdina <phrdina@redhat.com>
Date:   Fri Feb 5 16:17:35 2021 +0100

     vircgroup: use DBus call to systemd for some APIs

The error comes from virSystemdGetMachineByPID. The PID that shows up in
the above error message does not match the leader PID as reported by
machinectl.

This change fixes the error. Things seem to continue to work with
cgroupsv2 after this change.

https://gitlab.com/libvirt/libvirt/-/issues/182

Tested-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>