overcloud: add packer and rework initial implementation
Original implementation from https://gitlab.cri.epita.fr/cri/iac/packer
Initially-Authored-By: Jules Lefebvre jules@cri.epita.fr Co-Authored-By: Nicolas Froger nico@cri.epita.fr Signed-off-by: Nicolas Froger nico@cri.epita.fr