Comment 10 for bug 1712831

You can add/remove kernels to the guest by mounting them like via qemu-nbd.
To properly install boot it directly in kvm and then run dpkg.

That way I tested the mainline kernel above and the same way I switched back to [1].
With that I got correctly the older kernel:
  autopkgtest [13:48:11]: testbed running kernel: Linux 4.11.0-13-generic #19-Ubuntu SMP Thu Aug 3 15:13:04 UTC 2017

With that 3/3 runs with OVS 2.8 are good, so I think we can conclude this is a regression due to the kernel 4.12 update.

[1]: https://launchpad.net/ubuntu/+source/linux/4.11.0-13.19/+build/13193104