MAR-218: Switch to using fully-qualified collection names for all tasks:

- Ensures there is no ambiguity when invoking a module.

MAR-218: Fix linting errors for unnamed plays:

- All plays should be named at this point.
- Improve naming of some plays.
- Group some of the common tasks together to speed-up the prepare
step.
- Minor refactoring to make the prepare playbooks more consistent
across the roles.

MAR-129: Updated database role for new Molecule and Ansible versions:

- Fixed linting issues.
- Moved test variables into group_vars.
- Renamed the server which effectively tests the optional
parameters (mainly the backup).
- Updated tests to use correct mechanism for obtaining the list of
hosts on top of which the tests should be run.

MAR-128: Upgraded tests for database role:

- Switch to new Molecule configuration.
- Updated set-up playbook to use become: yes.
- Moved some preparatory steps outside of the main playbook (eases
idempotence tests).
- Updated tests to reference the yml inventory file.
- Updated tests to use new fixture (host instead of individual ones).
- Updated backup_server and backup_client configuration in order to
make the backup testing more generic (and easier to update for
future).