MAR-151: Drop rcconf workaround:

- The workaround was needed on Debian Jessie because the systemctl
is-enabled command did not behave correctly for SysV init scripts.
- Drop the installation of the rcconf package.
- Use the "enabled" parameter in service module instead.

MAR-151: Use 2048-bit DH parameter for IMAP server under Debian 10 Buster:

- Deploy a statically-generated DH parameter.
- Set-up DH parameter configuration based on Debian version.
- Implemented test for newly-generated file.

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: Fixing linting errors:

- Do not compare against booleans when value is already boolean in
"when" conditions.
- 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).

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 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-114: Updated task syntax for mail roles:

- Updated mail_server and mail_forwarder roles.
- 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-28: Impelmented general and SMTP-related tests for mail_server:

- Increased amount of memory in test instances to 768MB.
- Fixed playbook for runs against client test instances.
- Fixed typos and invalid settings in test playbook.
- Switched to expanded syntax in tasks used for deploying TLS keys and
certificates in order to avoid mangling of TAB characters.
- Fixed missing permissions set-up for Postfix main configuration file.
- Fixed deployment of Postfix master.cf configuration file to take into account
configurable virtual mail user.
- Implemented tests covering SMTP functionality.

MAR-28: Fixed minor issues in the mail_server tasks:

- Ensure command handler is excluded from linting checks.
- Fixed modes to use leading zero.

MAR-28: Implemented scaffolding for testing the mail_server role:

- Added Molecule configuration.
- Added test playbook.
- Restart Postfix for truststore changes.
- Added test data (private keys and certificates).
- Fixed small documentation inaccuracy.