Adding changes to OpenStack CPI for volume type.

Adding the following functionality to the OpenStack CPI:

* Switched from the compute to the volume API for persistent disk creation
 * Creating volumes from the compute API is deprecated in OpenStack
 * The volume API adds support for availability zones and volume type
* Adding availability zone support to the boot_from_volume functionality
* Added support for the new cloud_properties to set the volume_type from disk pool configuration

I see. It looks then like Fog is only set up to support the [V1 Block Storage API](http://developer.openstack.org/api-ref-blockstorage-v1.html#detail-d86e277), as that version does support those parameters.