Comment 2 for bug 1876301

Reviewed: https://review.opendev.org/724842
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=5913bd889f9d3dfc8d154415e666c821054c229d
Submitter: Zuul
Branch: master

commit 5913bd889f9d3dfc8d154415e666c821054c229d
Author: Lee Yarwood <email address hidden>
Date: Fri May 1 14:20:04 2020 +0100

    compute: Validate a BDMs disk_bus when provided

    Previously disk_bus values were never validated and could easily end up
    being ignored by the underlying virt driver and hypervisor.

    For example, a common mistake made by users is to request a virtio-scsi
    disk_bus when using the libvirt virt driver. This however isn't a valid
    bus and is ignored, defaulting back to the virtio (virtio-blk) bus.

    This change adds a simple validation in the compute API using the
    potential disk_bus values provided by the DiskBus field class as used
    when validating the hw_*_bus image properties.

    Closes-Bug: #1876301
    Change-Id: I77b28b9cc8f99b159f628f4655d85ff305a71db8