def ssh_cleanup_known_hosts!(hosts=[host, public_ip])
      hosts = [hosts] unless hosts.respond_to? :each
      hosts.compact.each do |name|
        system_run "ssh-keygen -R %s" % name
      end
    end
def ssh_cleanup_known_hosts!(hosts=[host, public_ip])
      hosts = [hosts] unless hosts.respond_to? :each
      hosts.compact.each do |name|
        system_run "ssh-keygen -R %s" % name
      end
    end
remove hostname and corresponding from known_hosts file.  Avoids warning when reusing elastic_ip, and
 less likely, if amazone reassigns ip.  By default removes both dns_name and ip