[DO NOT MERGE UNTIL 1.2.0 IS RELEASED] SELinux: Support for SELinux on RedHat platforms

Enable support for SELinux on RedHat platforms. The resource
SELinux will be activated before the installation of openstack
takes place.
I would rather see this code in cloud::init.
We try to maintain "roles" in manifests directory, and nstall is not a role AFIK.