Boot from volume

This change adds support for boot from volume to the OpenStack CPI.  To use, add the following property to the Micro BOSH or BOSH deployment manifest:

    cloud:
      plugin: openstack
      properties:
        openstack:
          boot_from_volume: true

Changes:
* Add a reference to the fog Volume API which supports created volumes with an imageRef
* Create a boot volume before creating the VM with the disk size specified by the flavor
* Add a block device mapping to the VM on creation to mount the new volume at /dev/vda
* Skip setting the "personality" property on VM creation since file injection is not supported with BFV
* Added test stubs for the Fog::Volume API to fix failures
* Added new tests for creating a boot volume and creating a VM using boot from volume