IS_DEBIANSECURITY_LXC: Don’t test older than Debian 9 containers

We use eLTS for Jessie without security, that has been archived and
signed with an expired key.

linux/evocheck.sh

@@ -205,8 +205,11 @@ check_debiansecurity_lxc() {
     if is_installed lxc; then
         container_list=$(lxc-ls)
         for container in $container_list; do
+            DEBIAN_LXC_VERSION=$(cut -d "." -f 1 < /var/lib/lxc/${container}/rootfs/etc/debian_version)
+            if [ $DEBIAN_LXC_VERSION -ge 9 ]; then
                 lxc-attach --name $container apt-cache policy | grep "\bl=Debian-Security\b" | grep "\bo=Debian\b" | grep --quiet "\bc=main\b"
                 test $? -eq 0 || failed "IS_DEBIANSECURITY_LXC" "missing Debian-Security repository in container ${container}"
+            fi
         done
     fi
 }