Update some cloud-init documentation (#331)

* Update some cloud-init documentation.

- Remove ds-identify.cfg configuration as that's no longer needed
- Change 'set-password' references to 'set_password' as the name has
  changed.
- Add a warning about disabled hostkey generation as this can result
  in a MITM
- Small typos

* Ensure existing set-password and set_password work
1 file changed