ipauser: Return generated random password

The random password is only returned if random is yes and user did not exist
or update_password is yes.

If only one user is handled by the module, the returned dict is containing
this dict:

  { "randompassword": "<the user random password>" }

If several users are handled by the module:

  { "<user>": { "randompassword": "<the user random password>" } }

This is related to issue #134 (ipahost does not return the random password)