selinux: Introduce ovirt-node-selinux sub-package

Previously the selinux module was compiled and installed during the KS
post section. Now it's generated at build time and installed during
installation.
Additionally to the extraction the policy module was also radically
simplified by dwalsh.

Change-Id: Ie1bfd54fd914ce740a93cd21ad6406e0e230d1d7
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>