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

- Updated role reference documentaiton.
- Updated role meta information.
- Updated tests.
- Replace the installation of libmariadbclient-dev-compat library with
atftp - the actual package is differently named under Debian Stretch
and Debian Buster (which would complicate the test without any
benefits).
- Drop the fix for root mail alias in Vagrant image - seems it's no
longer a problem.
- Split-up the test for web application user since it's not possible
to keep it all under one parametrised test due to differences in
assigned system UID numbers for Debian Stretch and Debian Buster.
- Make the test for web application user less dependant on what the
actual UID number is in case of default value. By default user
should be created as system user, which means its UID number should
be less than 1000.

MAR-150: Use fixtures for X.509 artefacts in the wsgi_website role:

- Removed the statically generated artefacts.
- Generate X.509 artefacts for tests using Gimmecert.
- Updated paths to point to generated artefacts.
- Introduced cleanup playbook for removing generated artefacts.

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

- Set the shell for application system account explicitly (workaround
for Debian bug 865762 in Stretch).
- Updated Molecule tests to cover Debian 9.
- Updated Molecule test preparation playbook to account for a number
of differences between Jessie and Stretch (mainly related to mailing
functionality).
- Renamed a couple of variables in test for sending out mails to make
it clearer what is being looked up as part of regex matching.
- Updated Molecule tests where certain paths depend on what Debian
release they are ran against.
- Split-up Jessie-specific tests into separate file.
- Remove the /bin/ss utility instead of renaming it (testinfra socket
tests do not work with /bin/ss).

MAR-129: Updated wsgi_website role for Ansible 2.5.x and new Molecule:

- Include top-level linting configuration in test configuration file.
- Fixed linting errors.
- Updated Ansible deprecation warnings related to use of
state=installed with apt module.
- Updated how hosts are being referenced in tests.
- Rename the 'ss' utility in order to properly test socket
connectivity as a workaround for Testinfra bug.

MAR-128: Upgraded tests for ROLE_NAME 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.
- Updated one of the tests that depend on output of pip freeze due to
new versions of packages coming out.
- Updated hostname to include Debian version (for future expansion).
- Renamded some test data to match new hostname.