MAR-218: Fix test instance preparation for php_website testing:

- Some of the tasks can only be run without errors on the spun up PHP
website instance due to (un)availability of ansible_eth0 variable.

MAR-218: Force handler execution during testing for consistency:

- Otherwise it can easily happen that some handlers never run, leaving
the machine in inconsistent state until they are run by hand.

MAR-218: Drop linting definitions from Molecule configuratin files:

- Molecule no longer natively supports running linters.
- Disable the Ansible Galaxy dependency installation (none of the
roles utilise this).

MAR-191: Drop support for Debian 10 Buster from the php_website role:

- Move some of the distribution release-specific information used in
tests into a fixture of its own. Make the code a bit cleaner/more
consistent.

MAR-189: Disable use of KVM paravirtualisation provider with Vagrant/VirtualBox:

- The VMs seem to randomly hang when the (KVM) clock source gets
initialised right after getting past the bootloader. Helps run the
tests in a way more reliable way.
- Should be removed if upgrading to latest kernel/VirtualBox versions
helps.

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

- Keep the mail alias step - it is still relevant for Debian Buster.

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

- Updated role reference documentaiton.
- Updated role meta information.
- Updated tests.
- Refactor the code to take into account differences in PHP-related
paths between 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.
- Drop the installation of libmariadbclient-dev-compat library - the
test is good enough without it, and the actual package is
differently named under Debian Stretch and Debian Buster (which
would complicate the test without any benefits).

MAR-150: Use fixtures for X.509 artefacts in the php_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-148: Disable Ansible's default of enforcing group names without dashes through Molecule configuration files:

The following links might be a useful read:

- https://github.com/ansible/ansible/issues/56930 (issues relaetd to
lack of docs, but many complaints and explanations within)
- https://groups.google.com/forum/#!topic/ansible-devel/bjAcM9ferIw

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

- Implemented the necessary changes related to differences between PHP
versions and related paths (PHP 5 vs PHP 7).
- 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).
- Use more specific host groups in tests.
- 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.

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

- Include global linting configuration file in tests.
- Fixed linting issues.
- Fix deprecation warnings from Ansible (for apt module and
state=installed).
- Updated how the hosts are being referenced within tests.

MAR-128: Upgraded tests for php_website 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 hostname to include Debian version.