Comment 9 for bug 1788226

Upgrade to proposed:
$ sudo apt install libvirt0 libvirt-daemon-system libvirt-daemon libvirt-clients
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-headers-4.15.0-29 linux-headers-4.15.0-29-generic linux-image-4.15.0-29-generic linux-modules-4.15.0-29-generic linux-modules-extra-4.15.0-29-generic linux-tools-4.15.0-29
  linux-tools-4.15.0-29-generic
Use 'sudo apt autoremove' to remove them.
Suggested packages:
  libvirt-daemon-driver-storage-gluster libvirt-daemon-driver-storage-sheepdog libvirt-daemon-driver-storage-zfs numad radvd auditd systemtap zfsutils pm-utils
Recommended packages:
  libxml2-utils libvirt-daemon-driver-storage-rbd
The following packages will be upgraded:
  libvirt-clients libvirt-daemon libvirt-daemon-system libvirt0
4 upgraded, 0 newly installed, 0 to remove and 32 not upgraded.
Need to get 4.100 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-daemon-system amd64 4.0.0-1ubuntu8.4 [80,7 kB]
Get:2 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-clients amd64 4.0.0-1ubuntu8.4 [596 kB]
Get:3 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt-daemon amd64 4.0.0-1ubuntu8.4 [2.174 kB]
Get:4 http://archive.ubuntu.com/ubuntu bionic-proposed/main amd64 libvirt0 amd64 4.0.0-1ubuntu8.4 [1.249 kB]
Fetched 4.100 kB in 2s (2.099 kB/s)
Preconfiguring packages ...
(Reading database ... 168385 files and directories currently installed.)
Preparing to unpack .../libvirt-daemon-system_4.0.0-1ubuntu8.4_amd64.deb ...
Unpacking libvirt-daemon-system (4.0.0-1ubuntu8.4) over (4.0.0-1ubuntu8.3) ...
Preparing to unpack .../libvirt-clients_4.0.0-1ubuntu8.4_amd64.deb ...
Unpacking libvirt-clients (4.0.0-1ubuntu8.4) over (4.0.0-1ubuntu8.3) ...
Preparing to unpack .../libvirt-daemon_4.0.0-1ubuntu8.4_amd64.deb ...
Unpacking libvirt-daemon (4.0.0-1ubuntu8.4) over (4.0.0-1ubuntu8.3) ...
Preparing to unpack .../libvirt0_4.0.0-1ubuntu8.4_amd64.deb ...
Unpacking libvirt0:amd64 (4.0.0-1ubuntu8.4) over (4.0.0-1ubuntu8.3) ...
Setting up libvirt0:amd64 (4.0.0-1ubuntu8.4) ...
Setting up libvirt-daemon (4.0.0-1ubuntu8.4) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for systemd (237-3ubuntu10.3) ...
Processing triggers for man-db (2.8.3-2) ...
Setting up libvirt-clients (4.0.0-1ubuntu8.4) ...
Setting up libvirt-daemon-system (4.0.0-1ubuntu8.4) ...
virtlockd.service is a disabled or a static unit, not starting it.
Setting up libvirt-daemon dnsmasq configuration.

Shutting down a 40*passthrough guest works finally!

$ sudo tail -f /var/log/libvirt/libvirtd.log | grep ainful
2018-08-23 13:03:33.315+0000: 73192: debug : virProcessKillPainfullyDelay:361 : vpid=73025 force=1 extradelay=80
2018-08-23 13:03:43.320+0000: 73192: debug : virProcessKillPainfullyDelay:380 : Timed out waiting after SIGTERM to process 73025, sending SIGKILL

Afterwards list is empty and the guest correctly gone:
$ virsh list
 Id Name State
----------------------------------------------------

The full set of automated tests ran already against the identical version from the PPA.

Setting SRU checks to Verified