leap node rm leaves ssh-fingerprints
when doing leap node rm amber, the files/ssh/known_hosts doesn't get updated. @ssh-keygen -f files/ssh/known_hosts -R hostname@ would remove the fingerprint and clean the known_hosts. It would leave a known_hosts.old in there, which we don't need, because should have their provider configuration on version control.
(from redmine: created on 2015-09-23)