MAR-26: Implemented tests and fixes ldap_server role:

- Use static network configuration in order to make it easier to test
connectivity from dedicated client.
- Added client machine for testing firewall.
- Added missing LDAP client configuration on instance used for testing of
mandatory options.
- Fixed name of server for backup testing purposes.
- Expanded a bit the cipher configuration for LDAP server for testing optional
parameters.
- Fixed wrongly populated Debian selections setting for LDAP organisation.
- Use templates for deploying LDAP TLS keys and certificates in order to avoid
Ansible munching the TAB characters.
- Implemented tests covering fully functionality of the role.