MAR-241: Implemented connection rate limit tests for the common role:

- Tweak some test machine parameters to have better test
sample representation.
- Tests heavily rely not being laggy to get the expected output. Tests
may need to get reworked a bit if they end up failing repeatedly
during test runs.

MAR-192: Switch to using NTP pools instead of servers:

- This is the recommended configuration by NTPsec, and also default on
Debian. Previuosly suggested values for servers have been pool
addresses in any case.

MAR-192: Switch to using NTPsec NTP server for increased security:

- This has for some time been a way better option, and it should also
provide for compatibility with Debian 12 Bookworm.

MAR-154: Drop support for Python 2.7 from the common role:

- This primarily concerns removal of pip requirements upgrade checks
for Python 2.7.
- The old Python 3-specific paths are getting deprecated, and the
Python 2 paths will be used instead.
- Set permissions on pipreqcheck directory explicitly (because of
deprecation testing).

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

- Drop the architecture suffix from all machines.
- Introduced a hack/patch for Ferm utility that disables use of legacy
iptables tools.
- Minor fixes around package name differences compared to older
distribution.
- Use versioned binary name for Python 2.7.. Bullseye does not
default/have /usr/bin/python pointing to Python 2.7 binary.

MAR-182: Added ability to specify input requirements for running pip package upgrade checks against helper virtual environments:

- These environments are used for running the package upgrade checks
themselves.

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

- Updated tests.
- Updated role reference documentation.
- Updated role metadata information.
- Refactored IP plan for the test machines for better separation
between different types of machines and versions.
- Parametrised tests for limited connectivity using the maintenance
mode.
- Don't use MariaDB compat package in tests - name differs between
Debian 9 and Debian 10, and relevant parameter is already getting
tested properly using the remaining packages.

MAR-150: Refactor the test for deployed CA certificates in common role:

- Use parametrisation to reduce code duplication.

MAR-150: Use Gimmecert for X.509 test fixtures in the common role:

- Drop the statically-generated X.509 certificates used for testing.
- Introduce fixture playbook in preparation phase that sets-up the
necessary certificates.
- Update the tests to use the fixture.
- Dynamically calculate the OpenSSL hash for CA certificate instead of
having the hard-coded value.
- Add the fixture artefacts to .gitignore files.

MAR-149: Minor syntax fixes for Python 3 in tests for common role:

- Do not use the unicode function (this still might break, need to
test it).
- Fix syntax used for catching exceptions within variables.
- Fix one small linting error related to row length.

MAR-149: Switch to using File.content_string instead of File.content in tests for all roles:

- The .content variant returns contents as bytes, while the
content_string returns a string (which is what is wanted in
practically all cases).

MAR-148: Fix test for the common role:

- Do some additional stripping on command outputs to get rid of extra
new lines.

MAR-129: Updated backup_server role tests:

- Move the 'ss' utility out of place in order to be able to test if
sockets are
open (seehttps://github.com/philpep/testinfra/pull/320).
- Updated tests to use correct mechanism for setting-up list of
machines where the tests should be run.

MAR-128: Upgraded tests for common role:

- Switch to new Molecule configuration.
- Updated set-up playbook to use become: yes.
- Moved some preparatory steps outside of the main playbook (easies
idempotence tests).
- Updated tests to reference the yml inventory file.
- Updated tests to use new fixture (host instead of individual ones).
- Switched to extracting IP address instead of hard-coding it in a
couple of tests.
- Fixed invalid indentation on task responsible for creating the
pipreqcheck Python virtual environment.