Added CLUSTER_NAME option

[dvalter]

I'm not sure about could it be the same as you wanted according to this issue, but I've created this implementation of cluster name for my own use. So I hope, it could be useful, maybe with some modifications. I doubt it's a good idea about manual adding ssh hosts to ~/.ssh/confi, but echo '...' >> ~/.ssh/config is even worse.

[kayrus]

New logic should be reflected in https://github.com/kayrus/deploy-vm/blob/master/remove_cluster.sh