spec: fix selinux-policy requirement for EL6

Change-Id: I910e04c5ac6e6a6f0991af7d144dca3ceba444c4
Bug-Url: https://bugzilla.redhat.com/1160808
Signed-off-by: Allon Mureinik <amureini@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/36018
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>