removing cluster member (WIP)

Remove node from a cluster. See https://trello.com/c/xarZEs6g/846-ha-support-removing-nodes-from-clusters

https://github.com/crowbar/barclamp-crowbar/pull/1011 (or its roxy version) is needed so the remove role get correctly deleted after it is used once.
It is not seen in UI. I expected this is needed because of the priority, but now I realize _remove roles are always done first. So I'll remove this.