MAR-23: Implemented tests for the database role:

- Updated test playbook to set-up backup_server as separate play in order to
avoid skipping of backup_client role.
- Updated test playbook to correctly set-up a single backup client.
- Do not manage permissions on /srv/ directory in database role. This can
interfere with backup client access.
- Do not manage permissions on /srv/ directory in ldap_server role. This can
interfere with backup client access.
- Implemented common tests.
- Implemented tests related to database backup.

MAR-23: Implemented initial scaffolding for testing database role:

- Added Molecule configuration.
- Implemented basic playbook for setting-up the two instances used for testing
mandatory parameters and backups.
- Added data necessary for setting-up all roles.
- Updated database_serve role Molecule configuration not to depends on the
Ansible Galaxy.