[RFE] make sushy-tools support OStack VMs that have been booted from volume or snapshot

[Adam Rozman]

The issue is that whenever a sushy tools tries to list the available nodes there is a failure when sushy-emulator finds a VM that was not booted from image instead it was booted from volume.

The issue is suspected to be here:
https://github.com/openstack/sushy-tools/blob/master/sushy_tools/emulator/resources/systems/novadriver.py#L254

In order to properly fix this issue a simple bug fix is not enough, the Sushy-tools nova driver
lacks the ability to support VMs that have been booted from volume or snapshot. Sushy-tools needs to have access to the boot image of the OStack instance in order to determine the boot mode and the secure boot requirement.

I propose implementing support for machines that have been booted from volumes or snapshots and in addition to that I propose implementing the functionality to traverse "chain"s of volume copies to be able to dig down to the volume or snapshot that has the bootable image reference .

[Adam Rozman (rozzix)]

Implementation of my proposal: https://review.opendev.org/c/openstack/sushy-tools/+/912113

[Iury Gregory Melo Ferreira (iurygregory)]

Marking as triaged and medium, but we need to see with the community about the approach =)