MAR-218: Force handler execution during testing for consistency:

- Otherwise it can easily happen that some handlers never run, leaving
the machine in inconsistent state until they are run by hand.

MAR-218: Drop linting definitions from Molecule configuratin files:

- Molecule no longer natively supports running linters.
- Disable the Ansible Galaxy dependency installation (none of the
roles utilise this).

MAR-239: Dropped support for Debian 11 Bullseye from the backup_client role:

- Switch to using Paramiko instead of pexpect backend (therefore
avoiding using the external SSH client binary).

MAR-192: Added support for Debian 12 Bookworm to backup_client role:

- Drop the orphan config file for backup server helper.

MAR-191: Drop Debian 10 Buster support for the backup_client role:

- Internal parameter for Python's pexpect package is no longer
required - newer versions of Debian have fully switche to using the
Python 3 version of it for duplicity.
- Fix prepare playbook task to iterate over list of backup users
instead of hard-coding the values.
- Drop the directory set-up task that seems to serve no purpose (some
leftover from previous refactoring most likely.
- Update supported version information in docs and metadata.

MAR-189: Disable use of KVM paravirtualisation provider with Vagrant/VirtualBox:

- The VMs seem to randomly hang when the (KVM) clock source gets
initialised right after getting past the bootloader. Helps run the
tests in a way more reliable way.
- Should be removed if upgrading to latest kernel/VirtualBox versions
helps.

MAR-189: Added support for Debian 11 Bullseye to backup_client role:

- Duplicity on Buster and Bullseye uses different Python version (2 vs
3), install the correct Python pexpect package.
- Switch the helper backup server to using Bullseye, and tweak its
SSHD configuration accordingly.

MAR-189: Refactor hostname pattern for backup_client role (buster/bullseye/bookworm):

- Multiple releases one after the other have names that begin with
letter b, making it necessary to use more than just one letter.
- Use full distro codename, but shorten the parameters to param in
order to avoid issues related to 32-character username limits (when
bak-HOSTNAME user gets created).
- Drop some leftover references to Debian Stretch.
- Drop the arch from hostnames - default is to use 64-bit boxes
anyway.

MAR-181: Drop support for Debian 9 Stretch from the backup_client role:

- Provide more details on use of pexpect+sftp backed for
Duplicity (backend has to be used on Debian 10 Buster as well, not
just Debian 9 Stretch).
- Switch to using IPs from VirtualBox default allowed host-only
network subnets.

MAR-151: Added support for Debian 10 Buster to backup_client role:

- Updated tests.
- Refactored one of the test to determine hostname dynamically.
- Update role reference documentation.

MAR-152: Drop support for Debian 8 Jessie from the backup_client role:

- Simplify the invocation of GnuPG commands (since we don't have to
massage output formats depending on distribution version anymore).

MAR-148: Disable Ansible's default of enforcing group names without dashes through Molecule configuration files:

The following links might be a useful read:

- https://github.com/ansible/ansible/issues/56930 (issues relaetd to
lack of docs, but many complaints and explanations within)
- https://groups.google.com/forum/#!topic/ansible-devel/bjAcM9ferIw

MAR-129: Updated Molecule configuration for the backup_client role:

- Updates necessary for use with Molecule version 2.14.
- Reference custom yamllint configuration file with custom rules.
- Fix YAML linting errors in Molecule's own files.

MAR-128: Upgraded tests for backup_client 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 SSH deployment to have chroot the users for a
bit easier set-up, and updated relevants playbooks/tests for this
purpose.