Fix disabling of SELINUX

Per the [Redhat documentation](https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/ch-The_sysconfig_Directory.html#s2-sysconfig-selinux) `/etc/sysconfig/selinux` is a symlink to `/etc/selinux/config`. We only need to change `/etc/selinux/config`. In addition, future changes to `/etc/sysconfig/selinux` may **not** be seen by the system as it reads `/etc/selinux/conf` on startup. The symlink appears to exist in RHEL 7 beta as well.