+++ This bug was initially created as a clone of Bug #1721433 +++

Description of problem: 

Sriov instance's spawn fails if additional properties "hw_vif_model & hw_disk_bus" in image

If we add the below metadata properties to image, and any VM launched with this image is moving to ERROR state due to failure of SRIOV port binding

~~~  
  hw_vif_model  = virtio
  hw_disk_bus = virtio
~~~


Error Message:-

u'message': u"unsupported configuration: Unknown PCI device <driver name='vhost'/> has been specified", u'code': 500, u'details': u'  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 1862, in _do_build_and_run_instance\n    filter_properties, request_spec)\n  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2142, in _build_and_run_instance\n    instance_uuid=instance.uuid, reason=six.text_type(e))\n


The above is strange as why would a Sriov instance have 'vhost' as a driver? A sriov interface should be seen as vfio device in libvirt.

Version-Release number of selected component (if applicable):

RedHat OpenStack Version 13.0


How reproducible: 


Steps to Reproduce:
1. Add additional property to image:-

~~~  
  hw_vif_model  = virtio
  hw_disk_bus = virtio
~~~

2. Spawn a sriov instance


Actual results:

Instance spawn is failing:-
~~~
u'message': u"unsupported configuration: Unknown PCI device <driver name='vhost'/> has been specified", u'code': 500, u'details': u'  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 1862, in _do_build_and_run_instance\n    filter_properties, request_spec)\n  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2142, in _build_and_run_instance\n    instance_uuid=instance.uuid, reason=six.text_type(e))\
~~~


Expected results:

Instance spawn should not fail.

Additional info: