Make prescript template RHEL-7 aware
Make prescript template RHEL-7 aware

Netns checking make no sense for RHEL-7. We also don't have openstack-selinux
package yet for RHEL-7.

Change-Id: Ie12ca2700d1817b4c6e3425229d3259fff595810

openstack/packstack,palmer159/openstack-test,xbezdick/packstack,stackforge/packstack,mahak/packstack,imcsk8/packstack,fr34k8/packstack,mahak/packstack,stackforge/packstack,imcsk8/packstack,stackforge/packstack,fr34k8/packstack,mahak/packstack,palmer159/openstack-test,xbezdick/packstack,xbezdick/packstack,fr34k8/packstack,palmer159/openstack-test,imcsk8/packstack,openstack/packstack,openstack/packstack