Enable support for SELinux on RHEL family OS

[dereknola]

As pointed out in #199 (comment), while the SELinux rpms are now downloaded by the K3s install script, we still are disabling SELinux on Redhat OS based distros https://github.com/k3s-io/k3s-ansible/blob/master/roles/prereq/tasks/main.yml#L2.

We need to remove that and properly ensure that redhat selinux support works as intended.