Comment 5 for bug 1780138

Reviewed: https://review.opendev.org/663677
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=db40cc44cbad32353510819c0aee1d0a3c9e4357
Submitter: Zuul
Branch: stable/stein

commit db40cc44cbad32353510819c0aee1d0a3c9e4357
Author: Lee Yarwood <email address hidden>
Date: Tue Jun 4 11:57:18 2019 +0100

    libvirt: Use SATA bus for cdrom devices when using Q35 machine type

    The Q35 machine type no longer provides an IDE bus and will need to use
    a SATA bus to attach legacy devices such as cdroms. More details can be
    found in the following related bug:

    Don't assume the guest machine type to be of 'pc'
    https://bugs.launchpad.net/nova/+bug/1780138

    This change now ensures the blockinfo.get_disk_bus_for_device_type
    method will now return "sata" as the bus type when the Q35 machine type
    is used for cdrom devices on QEMU or KVM hosts that are not PPC, S390 or
    AArch64 based.

    To enable this the _get_machine_type method has been extracted from the
    Libvirt driver into the Libvirt utils module. This method has also been
    simplified through the removal of the caps parameter, replaced with
    calls to the get_arch utility method and additional extraction of
    architecture specific defaults into the existing
    get_default_machine_type utility method.

    Related-bug: 1780138
    Closes-bug: 1831538
    Change-Id: Id97f4baddcf2caff91599773d9b5de5181b7fdf6
    (cherry picked from commit 527c452a6fc05a316eb8121796f761af97522772)