Directly expose all passlib.hash supported hashes, using a `passwd-`
prefix. For example, to access `sha256_crypt`, use `passwd-sha256-crypt`
option name.

  [secret]
  recipe = slapos.cookbook:generate.password

  [config-file]
  hashed-password = ${secret:passwd-sha256-crypt}

This changes the format of storage-path, it used to be the password in
plain text, it is now a mapping also containing hashed passwords, to
have the same hashed passwords for each buildout run.

This needs collaboration from publish_early recipe, because .pop(k) does
raised a KeyError with the dict.__missing__  approach.