Add role prefix to role specifig variable to avoid conflicts when
using multiples role on the same machine on the same play.

(IcingaWeb2) LDAP:

- procedure to automatically issue service credetinals to authenticate
  with the ldap server.

- starttls secured ldap connection with service account.

- use of the variable `base_dn` instead of hard-coded values in config
  files.

(IcingaWeb2) CONFIGURATION:

- fixed rsync parameters.

- resource renaming.

- Update to 18.0.4
- Version defined as variable in defaults/mail.yaml

Now it's possible to configure LDAP with servers that only support
plain-text authentication over insercure channels.

Role to configure nextcloud with LDAP User backend.

First test passed.

New modules:

- occ:
  set coniguration values using `php occ` nextcloud command-line tool.