MAR-232: Switch to using IP addreses in firewall rules for mail_forwarder role:

- Perform lookups on managed machine for the passed-in SMTP relay
host, and use those values when populating the firewall rules.

MAR-192: Fix missing dnspython library as requiremnts for running the roles:

- Turns out there is still one usage left in the mail_forwarder role.
- It might be a good idea to try to get rid of that single usage to
make the firewall coming up more reliable during boot time.

MAR-192: Get rid of the dnspython requirement, and document netaddr requirement:

- This is the result of previous deprecation of using resolvable names
for setting-up the list of allowed incoming connections when in
maintenance mode.

MAR-192: Upgrade documentation build requirements:

- Current requiremetns no longer seem to work with Python 3.9. Time to
bump up the Sphinx version.

MAR-194: Use IP addresses instead names for maintenance allowed connections:

- Less ambigious. Solves problems around names being resolvable to
different IPs depending on what DNS server is used.
- Parameter renamed to better represent what is specified.
- Updated requirements to allow execution of ipv4/ipv6 filters.
- Pin the rich requirement to a lower version for compatibility
reasons.
- Implement tests for IPv6 connectivity tests.
- Improve rendering of base rules (indentation).

MAR-193: Updated requirements file for up-to-date version of Python:

- Primarily required in order to run Gimmecert in tests.

MAR-158: Refactor ldap_server TLS-related tests to use nmap:

- Updated requirements to include defusedxml for safe parsing of XML
reports from nmap.
- Install nmap as part of preparation step.
- Refactored tests for TLS to use nmap ssl-enum-ciphers script for
listing available TLS versions and ciphers.

MAR-149: Update requirements to Molecule 2.22:

- Updated requirements to use Molecule 2.22.
- Updated requirements to include pip and setuptools (to avoid
breakages related to use of pip-tools).

MAR-134: Updated requirements:

- Remove workaround for broken pytest.
- Updated all requirements.

MAR-129: Updated requirements:

- Introduce Sphinx as requirement (need for building documentation).
- Updated requirements to Ansible 2.5.4 with dependencies.

MAR-129: Updated Molecule to version 2.12.0:

- Updated Molecule to version 2.12.0, alongside its requirements.
- Fixed tests for preseed role to account for new paths on destination
servers (change in Molecule).
- Updated wsgi_website test for pacakges installed in Python virtual
environment.

MAR-128: Starting to move towards Molecule 2.x:

- Updated requirements and its input file, primarily for use of
Molecule 2.4.x.
- Updated gitignore to exclude some additional artefacts produced by
Molecule 2.x.

MAR-125: Switching to Ansible 2.3.x:

- Updated documentation to reference only Ansible 2.3.x, removing mentions of
Ansible 1.9.x, and removing comments related to delayed switch to Ansible 2.x.
- Updated usage instructions to use Ansible 2.3.x.
- Updated pip requirements and its input file to use up-to-date versions of
Ansible and Molecule.
- Updated test site Ansible configuration to use pipelining.
- Fixed missing brackets in test site tls.yml playbook for "with_items.

MAR-30: Added documentation related to development:

- Moved existing test site documentation under the new 'Development' chapter.
- Added instructions for preparing development environment.
- Added instructions for running Ansible role tests.
- Added requirement input and txt files for use with pip-tools.