Add ha-cluster-remove remote command or similar

[tserong]

Commit 6daed36 ensures the remote rm -f is run inside bash. It would arguably be slightly better if we added a ha-cluster-remove remote command (or something like that, exact nomenclature TBD), similar to the way we have ha-cluster-init csync2_remote when adding nodes. This new command would both stop corosync and remove the config files on the remote host, thus needing only one ssh invocation instead of two and ensuring commands executed on the remote host are logged there rather than on the originating host.