Comment 13 for bug 1878973

Test results:
1. ensured we had the full matrix in place
2. ensured guest-agent was running fine in guest
3. issued virsh qemu-agent-command $rel '{"execute": "guest-shutdown"}'

1) Host: Q 2.11 L 4.0 (Bionic) - G 2.11 (Bionic)
2) Host: Q 4.0 L 5.4 (Eoan) - G 2.11 (Bionic)
3) Host: Q 4.2 L 6.0 (Focal) - G 2.11 (Bionic)
4) Host: Q 2.11 L 4.0 (Bionic) - G 4.0 (Eoan)
5) Host: Q 4.0 L 5.4 (Eoan) - G 4.0 (Eoan)
6) Host: Q 4.2 L 6.0 (Focal) - G 4.0 (Eoan)
7) Host: Q 2.11 L 4.0 (Bionic) - G 4.2 (Focal)
8) Host: Q 4.0 L 5.4 (Eoan) - G 4.2 (Focal)
9) Host: Q 4.2 L 6.0 (Focal) - G 4.2 (Focal)

Test a - shutdown functionality:
- 1-9: shutting down correctly
- 1-3,7-9: showed "error: Guest agent is not responding: Guest agent disappeared while executing command"
- 4-6: showed "error: Guest agent is not responding: Guest agent not available for now"

So the missing response warning doesn't seem to be new, and OTOH shutdown works fine on all of them.

In regard to the assert that we were looking for:
Test b - the assert
1,4,7: no assert
2-3,5-6,8-9: the assert triggers in the logs

It seems to NOT depend on the host version of qemu/libvirt.
It affects Eoan as well, and given the changes we see it seems [2] was the change that introduced this assert to be hit.

[2]: https://git.qemu.org/?p=qemu.git;a=commit;h=781f2b3d1e5e