libvirt: swtpm_ioctl is required for vTPM support

[Takashi Kajinami]

Description
===========
Libvirt uses swtpm_ioctl to shutdown the swtpm process at VM termination, because QEMU does not send shutdown command.
However the binary is not included in the required binaries (swtpm and swtpm_setup, at the time of writing) checked by libvirt driver. So users can use vTPM support without binaries, which leaves swtpm processes kept running.

Steps to reproduce
==================
* Deploy nova-compute with vTPM support
* Move swtpm_ioctl from PATH
* Restart nova-compute

Expected result
===============
nova-compute fails to start because swtpm_ioctl is missing

Actual result
=============
nova-compute starts without error and reports TPM traits.

Environment
===========
This issue was initially found in master, but would be present in stable branches.

Logs & Configs
==============
N/A

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/908546

[Takashi Kajinami (kajinamit)]

The relevant commit in libvirt is https://github.com/libvirt/libvirt/commit/69122bc2f1a4f33a019e4e939bb12687a0f527d3 .

Currently libvirt reports availability of emulated vTPM only when swtpm_ioctl exists, but the logic in nova is not aligned with it.

[Takashi Kajinami (kajinamit)]

Ignore my previous comment...

Usage of swtpm_ioctl was addedx when support for external TPM, run by swtpm, was added in https://github.com/libvirt/libvirt/commit/2a606b863ebdc0a74e87c453bb9b76278a72d13b .