requirements-tests.txt

Currently, upstream CI test documentation against different Ansible
versions, but playbook tests are only executed with Ansible 2.9 series.
This patch add support for running playbook tests against Ansible 2.9,
ansible-core 2.11, and against latest version of Ansible.

As running all the tests for every PR would take too long, the tests
for every PR use only Anisble 2.9, and are executed on Fedora-latest
and CentOS 7 and 8.

A new pipeline for nightly tests was added, which runs the tests in the
same distros, using Ansible 2.9, latest and Ansible-core 2.11.