Update builder Makefile to enable SELinux and run the relabelling.
Update builder Makefile to enable SELinux and run the relabelling.

Thanks: rwmjones in #libguestfs for help and discussion.

vvaldez/vagrant-builder,gpjonesii/vagrant-builder,gpjonesii/vagrant-builder,purpleidea/vagrant-builder,vvaldez/vagrant-builder,purpleidea/vagrant-builder