vircgroup: introduce virCgroupV2DetectPlacement
vircgroup: introduce virCgroupV2DetectPlacement

If the placement was copied from parent or set to absolute path
there is nothing to do, otherwise set the placement based on
process placement from /proc/self/cgroup or /proc/{pid}/cgroup.

Signed-off-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

crobinso/libvirt,eskultety/libvirt,jardasgit/libvirt,libvirt/libvirt,libvirt/libvirt,nertpinx/libvirt,olafhering/libvirt,eskultety/libvirt,crobinso/libvirt,eskultety/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,libvirt/libvirt,jardasgit/libvirt,olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,eskultety/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,zippy2/libvirt,nertpinx/libvirt,jfehlig/libvirt,zippy2/libvirt,jardasgit/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,zippy2/libvirt,fabianfreyer/libvirt,zippy2/libvirt,fabianfreyer/libvirt,olafhering/libvirt,crobinso/libvirt,jardasgit/libvirt,andreabolognani/libvirt,crobinso/libvirt,eskultety/libvirt,libvirt/libvirt,jfehlig/libvirt