code: public void saveHostKey(Computer host, HostKey hostKey) throws IOException {
          XmlFile xmlHostKeyFile = new XmlFile(getSshHostKeyFile(host.getNode()));
          xmlHostKeyFile.write(hostKey);
          cache.put(host, hostKey);
      }
docs: Persists an SSH key to disk for the requested host. This effectively marks
  the requested key as trusted for all future connections to the host, until
  any future save attempt replaces this key.
  @param host the host the key is being saved for
  @param hostKey the key to be saved as the trusted key for this host
  @throws IOException on failure saving the key for the host