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-155: Make the preseed_directory parameter in the preseed role mandatory:

- Updated the preseed role.
- Removed default value for the parameter.
- Updated tests.
- Updated role reference documentation.
- Updated release notes.

MAR-129: Updated preseed role for Ansible 2.5.x and new Molecule:

- Include top-level linting configuration in test configuration.
- Fixed linting errors.
- Moved test playbook variables into group_vars.
- Updated how hosts are referenced in tests.

MAR-128: Upgraded tests for preseed 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).
- Switched to extracting hostname instead of hard-coding it in a
couple of tests.
- Introduced additional hosts for testing on different Debian
versions.