WIP/DNM: Make fat image usable on boot for compute nodes

[sjpb]

Things which need to be done on boot to make the fat image usable for a compute node immediately (i.e. no ansible):

• munge key: written to file by ansible
• control name/addr for slurm - written to file by ansible
• FreeIPA: We run the renrolement stuff from Ansible at the moment.
• services start:
  • cuda role (not enabled fat image anyway) would run in full during fat image build sets nvidia-persistenced enabled
  • munge
  • slurmd
  • node-exporter: is already enabled in image build
• etc_hosts: At least for arcus where internal dns doesn't work. And this is hard cause we don’t know the IPs until we have created the hosts (or at least ports)
• also potentially resolv_conf, proxy
• also need to think about systemd role / common defaults

See also main...experiment/bootable-compute