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.

MAR-24: Implemented tests for 'database_server' role:

- Added Molecule configuration for single platform and instance.
- Added test playbook that deploys database_server role for testing.
- Fixed mode setting by appending leading zero.
- Ignore task that immediatelly restarts MariaDB database server.
- Implemented tests for the role covering full functionality.