Comment 12 for bug 1629972

I've verified that networking.service does not take down 'lo' interface
with the proposed version in yakkety (0.8.13ubuntu3).

Below, first I show the problem in 0.8.13ubuntu2 and then install
the proposed version and show it fixed.

$ lxc launch ubuntu-daily:yakkety y1
$ sleep 10
$ lxc exec y1 /bin/bash

% dpkg-query --show ifupdown
ifupdown 0.8.13ubuntu2

## show only things that are up (note output has LOOPBACK,UP,LOWER_UP)
% ip link show dev lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

% ip address show dev lo up
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever

## Stop the service and show lo link is down (no 'UP' or 'LOWER_UP').
% systemctl stop networking.service
% ip link show dev lo
1: lo: <LOOPBACK> mtu 65536 qdisc noqueue state DOWN mode DEFAULT group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
% out=$(ip address show dev lo up); [ -n "$out" ] && echo "$out" || echo empty
empty

## Now enable proposed, install update, reboot and show.
% rel=$(lsb_release -sc)
% echo "deb http://archive.ubuntu.com/ubuntu $rel-proposed main" |
    sudo tee /etc/apt/sources.list.d/proposed.list
% sudo apt update -qy && sudo apt install -qy ifupdown </dev/null
% dpkg-query --show ifupdown
ifupdown 0.8.13ubuntu3
% sudo reboot

## in rebooted system
% ip link show dev lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
% ip address show dev lo up
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
% systemctl stop networking.service
% ip link show dev lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
% out=$(ip address show dev lo up); [ -n "$out" ] && echo "$out" || echo empty
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever