Find stable urls for lxd container tests

[jonringer]

Please find stable urls for the lxd container tests

nixpkgs/nixos/tests/lxd.nix

Line 10 in 6aeccf3

alpine-meta = pkgs.fetchurl {

these fail to download now and are causing test failures:

trying https://uk.images.linuxcontainers.org/images/alpine/3.11/i386/default/20200608_13:00/lxd.tar.xz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

trying https://uk.images.linuxcontainers.org/images/alpine/3.11/i386/default/20200608_13:00/rootfs.tar.xz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
created 5239 symlinks in user environment
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (22) The requested URL returned error: 404 Not Found
error: cannot download lxd.tar.xz from any mirror

cc @Patryk27

[Patryk27]

Thanks for pinging - I will fix it later today :-)