OpenStack zones for volume

Current OpenStack driver where i use boot_from_volume option use VM zone name for volume - this not work because volume zones is other thing that VM zones if you want to use specified zones.

``` python
boot_from_vol = [{'boot_index': 0,
'uuid': image.id,
'volume_size': FLAGS.openstack_volume_size,
'source_type': 'image',
'destination_type': 'volume',
'delete_on_termination': True}]
```

We wan't to change it to create volume in disk zone and give this volume for booting there VM.
We need to add zone in disk_spec.