nspawn: chown() the legacy hierarchy when it's used in a container

[flokli]

This fixes nspawn container with older systemd failing to start.

(cherry picked from commit 6132e1c)

See:
systemd#10104
NixOS/nixpkgs#47253

[Mic92]

@globin @fpletz I tested this locally with:

systemd.package = pkgs.systemd.overrideAttrs (old: {
  patches = [
    (pkgs.fetchpatch {
      url = "https://github.com/NixOS/systemd/commit/6f7a429e9b0ed2bc1e7e5c24ea5bc70d72c36962.patch";
      sha256 = "0qxghr0vzfkxsb61xmzy5x5lfws6fyvxpcggq4hp406waa3ng1jc";
    })
  ];
 });

and an ubuntu container. Please merge.

[fpletz]

Thanks!