Role user_and_groups: end users enrolement

Design of several facilities to ensure end user enrolement and password definition. We want:

• when we don't have a user's ssh public key (for instance for desktop users), we want to be able to:
  • send an email to the user whith a (not too long) temporary password,
  • disable password access and let the user set her password on first login
  • eventually let a guest account without passord,
• start managing new user module's parameters in recent ansible releases: password_expire_max``, password_expire_minandumask`