determine predictable network names, Closes: #834817

currently booting dracut's initrd with FAI still gives eth0 when using
stretch, maybe udevadm must be called to rename the network devices

examples/simple/scripts/DEBIAN/30-interface

@@ -4,6 +4,20 @@ error=0; trap 'error=$(($?>$error?$?:$error))' ERR # save maximum error code
 
 if ifclass DHCPC && [ $FAI_ACTION = "install" -o $FAI_ACTION = "dirinstall" ]
 then
+
+    # determine predictable network names
+    fields="ID_NET_NAME_FROM_DATABASE ID_NET_NAME_ONBOARD ID_NET_NAME_SLOT ID_NET_NAME_PATH ID_NET_NAME_MAC"
+    for field in $fields; do
+	name=$(udevadm info /sys/class/net/$NIC1 | sed -rn "s/^E: $field=(.+)/\1/p")
+	if [[ $name ]]; then
+            NIC1=$name
+            break
+	fi
+    done
+    if [[ ! $name ]]; then
+	echo "$0: error: could not find systemd predictable network name. Using $NIC1."
+    fi
+
     cat > $target/etc/network/interfaces <<-EOF
 	# generated by FAI
 	auto lo $NIC1