Volume boot test uses new block device syntax

This patch adds a new test that tests the volume boot with the new block
device mapping syntax that was added to Nova in Havana.

For more details on the v2 block device mapping syntax see the following
Wiki page: https://wiki.openstack.org/wiki/BlockDeviceConfig

Change-Id: Ie15d62fded79dd19e896f6317123597f70ed3f6e
Merge "Volume boot test uses new block device syntax"