"nova evacuate" always fails if an instance has one or more iSCSI multipath cinder-volumes

Issue

• "nova evacuate" always fails if an instance has one or more iSCSI multipath cinder-volumes.

  Sample log is below

  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 6391, in _error_out_instance_on_exception
    yield
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2700, in rebuild_instance
    bdms, recreate, on_shared_storage, preserve_ephemeral)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2739, in _do_rebuild_instance_with_claim
    self._do_rebuild_instance(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2847, in _do_rebuild_instance
    self._rebuild_default_impl(**kwargs)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2600, in _rebuild_default_impl
    detach_block_devices(context, bdms)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2824, in detach_block_devices
    destroy_bdm=False)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 4734, in _detach_volume
    connection_info = self._driver_detach_volume(context, instance, bdm)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 4687, in _driver_detach_volume
    self.volume_api.roll_detaching(context, volume_id)
  File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 204, in __exit__
    six.reraise(self.type_, self.value, self.tb)
  File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 4675, in _driver_detach_volume
    encryption=encryption)
  File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 1272, in detach_volume
    self._disconnect_volume(connection_info, disk_dev)
  File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 1069, in _disconnect_volume
    driver.disconnect_volume(connection_info, disk_dev)
  File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/volume/iscsi.py", line 93, in disconnect_volume
    self.connector.disconnect_volume(connection_info['data'], None)
  File "/usr/lib/python2.7/site-packages/oslo_concurrency/lockutils.py", line 254, in inner
    return f(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/os_brick/initiator/connector.py", line 565, in disconnect_volume
    raise exception.VolumeDeviceNotFound(device=host_devices)