Comment 9 for bug 1737640

Tested that on a "broken" environment (after a reboot with a broken package):

root@maas-xenial3:~# apt install ubuntu-fan
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
1 upgraded, 0 newly installed, 0 to remove and 94 not upgraded.
Need to get 36.4 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 xenial/main amd64 ubuntu-fan all 0.12.8~16.04.2~rc1 [36.4 kB]
Fetched 36.4 kB in 0s (0 B/s)
(Reading database ... 60144 files and directories currently installed.)
Preparing to unpack .../ubuntu-fan_0.12.8~16.04.2~rc1_all.deb ...
Unpacking ubuntu-fan (0.12.8~16.04.2~rc1) over (0.12.8~16.04.1) ...
Processing triggers for systemd (229-4ubuntu19) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up ubuntu-fan (0.12.8~16.04.2~rc1) ...

# after a reboot with a broken package an address was present but the interface was not considered as "configured" by ifupdown - had to manually delete an address to avoid RTNETLINK answers: File exists on ifup

root@maas-xenial3:~# ip a d dev ens3

root@maas-xenial3:~# ifdown ens3
ifdown: interface ens3 not configured

root@maas-xenial3:~# ifup ens3

root@maas-xenial3:~# ip a s
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 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:82:7d:16 brd ff:ff:ff:ff:ff:ff
    inet brd scope global ens3
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fe82:7d16/64 scope link
       valid_lft forever preferred_lft forever

# all good
root@maas-xenial3:~# ifdown -a
root@maas-xenial3:~# ifup -a