With a 3-node control-plane, ABI waits for 2 of the nodes to come up and join the cluster before rebooting the bootstrap/rendezvous node.

With a 4- or 5-node control-plane, ABI waits for... 2 of the nodes to come up and join the cluster before rebooting the bootstrap/rendezvous node.

Previously (in OCPBUGS-41811) we made ABI wait for all workers to join before rebooting the bootstrap, because of a race condition that could prevent those nodes from coming up if assisted-service was gone. (This code is specific to ABI, because in a regular assisted install, assisted-service is still available even after the bootstrap is rebooted to become a control-plane node.)

We are likely vulnerable to the same potential race with 4- or 5-node control planes. We should wait for n-1 control-plane nodes to be available before reboot in the ABI case.