nova does not correctly support HW_DISK_BUS=sata or usb for kvm/qemu

Description
===========
The hw_disk_bus image metadata key
https://github.com/openstack/glance/blob/master/etc/metadefs/compute-libvirt-image.json#L13-L27
allows users to specify the bus to which guest hard disk images are attched for libvirt instances.

The valid values of hw_disk_bus are ["scsi","virtio","uml","xen","ide","usb","fdc","sata"]

The libvirt driver also defieds the list of valid buses per virt_type
here https://github.com/openstack/nova/blob/ef0ce4d692d28a7f5a0079e24acdbfe7d2767e8b/nova/virt/libvirt/blockinfo.py#L199-L206

   valid_bus = {
        'qemu': ['virtio', 'scsi', 'ide', 'usb', 'fdc', 'sata'],
        'kvm': ['virtio', 'scsi', 'ide', 'usb', 'fdc', 'sata'],
        'xen': ['xen', 'ide'],
        'uml': ['uml'],
        'lxc': ['lxc'],
        'parallels': ['ide', 'scsi']
        }

when setting this key to sata or usb instead of having the disk attached to the requested bus
the disk is attached to the scsi bus instead.

this is because in nova/virt/libvirt/blockinfo.py we map form the disk bus to a prefix
in get_dev_prefix_for_disk_bus
https://github.com/openstack/nova/blob/ef0ce4d692d28a7f5a0079e24acdbfe7d2767e8b/nova/virt/libvirt/blockinfo.py#L124-L143

then later we guess what the correct bus is from the prefix in get_disk_bus_for_disk_dev
https://github.com/openstack/nova/blob/ef0ce4d692d28a7f5a0079e24acdbfe7d2767e8b/nova/virt/libvirt/blockinfo.py#L297-L304

this mapping form disk bus to prefix is lossy as as sata/scsi and usb are all mapped to the sd prefix. so when we guess in get_disk_bus_for_disk_dev for kvm that resutin the incorrect value for images with hw_disk_bus=sata or hw_disk_bus=usb.

Steps to reproduce
==================
run devstack with default setting
source openrc

set hw_disk_bus=sata on image
e.g. openstack image set --property hw_disk_bus=sata my-image

boot a vm with that image
run virsh dumpxml on instance and check the disk bus.

Expected result
===============
instance boots and disk bus used matches hw_disk_bus image metadata value.
e.g. sata

Actual result
=============
instnace boots and disk bus used is scsi

Environment
===========
1. Exact version of OpenStack you are running. See the following
  stable/pike but this is present in master and has been an issue for 5 years
  since https://github.com/openstack/nova/commit/7be531fe9462f2b07d4a1abf6687f649d1dfbb89#diff-2701504299cd384f46791e08f1849defR293
incorrectly called get_disk_bus_for_disk_dev instead of useing the disk_bus varible.

2. Which hypervisor did you use?
   Libvirt + KVM

2. Which storage type did you use?
   default local image backend for nova.

3. Which networking type did you use?
   Neutron with OpenVSwitch.
   not related to this issue.