MAR-198: Implement removal of expired backups via backup_client role:

- In addition to expired backup removals, ensure that the backup
does not proceed if previous execution step has failed. This means
that pre-scripts now have to run without errors for the main backup
to kick-in.
- Could not use full _and_ chaining of duply. For example, if we have
A_and_B_and_C (where A/B/C are duply backup commands), if A
fails, B will be skipped, but C will still run because B has ran
without_errors.

MAR-191: Using pexpect+sftp still required for Duplicity backup:

- From what I can tell even Debian 11 Bullseye duplicyt has similar
limitation like the Buster version.

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: 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-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-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: Refactor handling of GnuPG backup client keyring:

- Don't use the include_tasks, it seems to cause more issues than it
helps (with linting etc).
- Directly reference all the relevant handlers as part of notification
instead.

MAR-148: Fix Ansible warnings for the backup_client role:

- Use length filter to check if optional parameter lists have been
supplied.
- Quote the crontab trigger times to avoid implicit conversion from
integer to string.

MAR-148: Fixing linting errors:

- Do not compare against booleans when value is already boolean in
"when" conditions.
- Use pipefail in conjunction with setting the shell to Bash when
extracting the backup encryption key IDs.
- Do not compare variables to empty strings in "when" conditions. This
change currently works only for complex variables (stuff can break
badly in case of simple variables in current default Ansible
configuration).
- Fix missing space in one of Jinja2 templates.

Noticket: Fix the invocation of GnuPG to use the --no-tty option:

- At least in some cases GnuPG would otherwise fail to run.

MAR-134: Fix Ansible warning about use of apt and with_items:

- The apt module can accept list of names already, and with_items is
considered to be deprecated in this regard (otherwise it would
end-up running one apt command per item).
- Changed multiple roles where apt was used together along with_items.

MAR-135: Switch to using run_handlers instead of handlers as variable:

- Updated all roles to now depend on run_handlers being set to True in
order to force execution of handlers.

MAR-129: Updated backup_client role tests:

- Update how the hosts are being referenced in tests (for limiting the
test runs).
- Use "state: present" for package presence/installation.
- Break-up long lines in tasks so they are under 160 characters
length.
- Fixed YAML linting issues.

MAR-114: Updated task syntax for backup roles:

- Updated backup, backup_client, and backup_server.
- Added and removed quoting where it makes sense.
- Switched to using expanded syntax (instead of one-liners).
- Updated ordering of arguments in task definitions.

MAR-108: Small fixes for backup_client role:

- Make sure that the /etc/duply/main/include file exists even if no backup
patterns (via backup role) have been provided).
- Fixed issue with backup_server_port not being used in the Duply configuration
file.

MAR-108: Applied linting fixes for backup_client role:

- Ignore the two handlers for Ansible lint checks since they are only called via
notify and if user explicitly requested so.
- Simplify the playbook by installing python-pexpect unconditionally on all
versions of Debian.
- Fixed a number of file mode parameters to use leading zero.

MAR-108: Updated tests for backup_server role:

- Refactored how the internal parameters for GnuPG binary name and length of
key ID used in Duply configuration is set-up (use defaults/main.yml instead of
set_facts module).
- Added Debian Stretch as supported platform to molecule tests.
- Replaced use of backup_server role for deployment with regular server with SSH
properly set-up.
- Use IP address for backup server instead of hostname for backup_client
configuration.
- Fixed key lookup for known hosts to use public keys (and not private keys).
- Added public keys of server for deployment in client known_hosts file.

MAR-108: Implemented initial boilerplate for backup_client tests:

- Fixed backup_client role handling of encryption keys.
- Fixed backup server URI (had too many forward slashes).
- Added Molecule instance configuration file for backup server, one backup
client for testing mandatory parameters, and one backup client for testing
optional parameters.
- Implemented playbook for setting-up the test instances.
- Added test data (SSH, GnuPG keys).
- Added dummy (stock) Molecule test file.