CI testing a request is successful.

`curl` on some distributions can return always a successful exit code,
even for 4xx HTTP responses which prompted a change to test the HTTP
status of the response directly.
Fix CentOS/RedHat provisioning.

RedHat uses SELinux, even on permissive, Ansible needs a pyhton package
to do shenanigans with SELinux.
Remove virtual host declaration from defaults.

As the document root varies between OS families, the default needs to be
sensible to that in order so that the `test.yml` playbook works properly
and is testable.