After booting all nodes, the bootstrap completes and the api moves, but everything else is stuck. 

    

4.20 with arbiter

    

easy. 2 for 2

    

    1. boot nodes form iso
    2. non rensezvous hosts reboot.
    3. nothing else happens
    

install continues and finishes

    

There is a workaround:
1. after the non-rendezvous hosts reboot. check the api address. once it moves you can reboot the original rendezvous host and it will join the cluster
2. reboot the the workers and they will join the cluster.