MAR-218: Improve mail server role test reliability:

- Introduce sleep after sending out mails in order to ensure that
Postfix has had enough time to process the messages.
- Relevant only for tests that take care of parsing the mail log.
- Solves the false negatives caused by timing issues.
- It might be a good idea down the line to implement some kind of
retry/backoff mechanism instead.

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

- Allow use of older versions of TLS on Bookworm for testing of
related optional parameters.
- Install the IMAP CLI testing tool under its own virtual environment
in order to avoid warnings and errors when trying to install it
globally under Debian 12 Bookworm.
- Update the lists of expected TLS protocols and ciphers.

MAR-189: Refactor test for additional SMTP server configuration:

- Use different override to avoid Postfix warnings about overridden
configuration option in the same file.

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

- Shorten the backup client username so it would be under 32
characters.
- Switch all helper VMs to using the Debian 11 Bullseye as well.
- Drop the architecture suffix from hostnames.
- Update the hostname for client VMs.
- Fix the incorrect format for the message ID used in various mail
delivery tests.

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

- Switch to using IPs from VirtualBox default allowed host-only
network subnets.
- Use Debian Buster for helper machines.
- Drop Stretch-specific code and tests.

MAR-151: Fix tests that fail due to differences between Debian Stretch and Debian Buster:

- Update the regex patterns used to locate deliveries via Dovecot.
- Enable verbose mode for gnutls-cli in one of the tests in order to
show the DH key size.
- Update the list of expected TLS ciphers for SMTP port 25 to account
for inclusion of additional ciphers in Debian Buster.
- Fix how the allowed relay IP is being fetched, because
host.ansible.get_variables method fails to resolve dynamic
variables.

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

- Updated role reference documentaiton.
- Updated role meta information.
- Updated tests.
- Improve handling of configured IP in tests to avoid hard-coding the
value in the relevant test for Postfix configuration file content.

MAR-163: Deduplicate test for certificate validity check configuration in mail_server role:

- Tests are already identical, they were probably kept separate by
mistake.

MAR-175: Update Postfix configuration, merging changes from Debian Buster stock installation and latest ISPmail tutorials:

- Added commented-out section for TLS parameters from Debian Buster
default configuration. This should slightly help with handling the
diff's in the future.
- Added a number of "missing" configuration parameters from the Debian
Buster stock configuration.
- Separate relay-related restrictions from spam-related restrictions.
- Updated configuration for RBLs.
- Updated default service definitions in the master.cf configuration
to be in-line with options defined in Debian Buster. This is
primarily revolving around the change to the chroot
option. Previously the default was to chroot the processes, while
new default is not to do so. This required marking a number of
services to be explicitly chroot'ed.
- Updated the submission service definition in master.cf configuration
file. Some minor changes were made, like switching to using the
smtpd_relay_restrictions instead of
smtpd_recipient_restrictions (better suited configuration option for
this use-case since it's not spam-related), being more explicit
around TLS being required for authentication.

MAR-158: Update default TLS ciphers configuration in the mail_server role:

- Updated the default value for parameter mail_server_tls_ciphers.
- Updated tests, making them explicitly test for enabled and disabled
ciphers.
- Refactored tests for TLS to use nmap ssl-enum-ciphers script for
listing available TLS versions and ciphers.
- Install nmap as part of preparation step.
- Updated role reference documentation.

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).

Noticket: Improve reliability for mail_server tests, detection of running ClamAV daemon:

The fixes mainly help with reliability of tests against the
mail_server role due to ClamAV not becoming available before the tests
get run. This normally is not a real issue in production (since the
daemon will become available farily quickly).

Changes made:

- Wait for ClamAV socket to become available in mail_server
role (otherwise mail delivery failures can happen).
- Increase memory used in mail server instances for testing to avoid
OOM killer kicking-in during tests.
- Introduce slight delay when running local alias tests to avoid race
condition.
- Formating fix in task that waits for ClamAV database to be
available.

MAR-148: Fixed tests for the mail_server role:

- Implement small workaround for sieve-connect invocations (due to
special treatment of 255 exit code by Testinfra itself).
- Fixed a couple of newline-related errors coming from command
outputs.

MAR-132: Added support for Debian 9 (Stretch) to mail_server role:

- Updated Molecule configuration to include set-up of additional
instances for testing.
- Updated configuration for test instances.
- Use separate clients in testing of Jessie/Stretch instances.
- Duplicate private keys/certificates for testing of mandatory
parameters on Debian 9.
- Refactored testing of mail deliveries (via swaks) to use
test-generated message ID - improves reliability and solves some
incompatibilities between swaks version in Jessie and Stretch.
- Updated tests for TLS testing to take into account newer OpenSSL
error/output messages. A bit of an ugly hack at the moment, but
beats duplicating tests for now.

MAR-129: Updated mail_server role for new Molecule and Ansible:

- Moved variables from test playbooks into group/host vars.
- Fixed linting errors.
- Reference custom top-level linting configuration file in tests.
- Fixed deprecation errors reported by Ansible.
- Updated how the hosts on which the tests should be run are
referenced.

MAR-128: Upgraded tests for mail_server 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.
- Fixed some linting issues.
- Renamed the hosts to make it easier to extend in future.
- Renamed some data files to ensure they correspond correctly to new
hostnames.
- Rewrote logic behind setting-up the /etc/hosts a bit, and expanded
the names to include the new hostnames.
- Updated a couple of tests to correspond to correct filenames (that
have been renamed).
- Updated a couple of tests to address the new server naming.
- Set explicitly the backup client username to avoid 32-charactr
limitation on Linux usernames.