MAR-29: Implemented tests for php_website role:

- Install some additional tools for testing everything.
- Updated test playbook to change allowed extensions for running PHP scripts on
parameters-optional.
- Updated error page to use correct extension for parameters-optional test
instance.
- Expanded rewrite configuration slightly for parameters-optional.
- Install libmariadb-client-lgpl-dev-compat to test mysql_config symlink
creation.
- Deploy a number of PHP pages used for testing if pages are served correctly.
- Set file permissions on deployed PHP FPM pool configuraiton files.
- Use expanded syntax when deploying TLS keys/certificates in order to avoid
issues with TAB mangling.
- Fixed set-up of Strict-Transport-Security header when HTTPS enforcement is
disabled.
- Added a number of PHP and static test pages.
- Wrote tests covering full functionality of the role.