Update docs

The docs have been updated to better explain how to lint.

Overall better

See the commits.

Consistency

This release includes:

• Rename of (internally used) variables to preceed {{ role_name }}_.
• Fix for Fedora Rawhide which uses python-3.
• Fix for lint rule 405

Lesser ist besser

This release features:

• Tests on less version of Ansible.
• Tasks are not skipped on Docker by default.
• Updated documentation.

Simpler is better

In order to make the tasks more readable and better maintainable, the variable structure has been improved.

no-gentoo

Gentoo has been removed from the tests, as it won't work in Travis because of timeouts.

Meta

Mostly meta fixes and cleanups. This means this role is ready for Galaxy 3.0.3 with quality assessments.

Integrated

On integration, an error was spotted, fixed in this release.

Ansible Fest 2018

All the goodness seen on Ansible Fest 2018, implemented into this role.

Firewalld

Using firewalld instead of iptables. Seems to work much more logical and ensure idempotency.