should not delete bootstrap cluster if pivot did not happen

Consider the following scenario (seen in my dev env):

• deploy from bootstrap.sh
• for some reason some unit don't deploy in mgmt cluster, on which the cluster-pivot-ready unit depends
• I fix the cause, using apply.sh to apply the fix
• at the end of the run apply.sh runs cleanup_bootstrap_cluster at the end and deletes the bootstrap cluster ...to early to let it time to actually do the pivot

I end up with a management cluster which hasn't pivoted, or not fully, and we possibly have no way to pivot.

The solution is to only let cleanup_bootstrap_cluster delete the bootstrap cluster only if the pivot Kustomization is Ready, and display an error if not.