Add a virtual PowerDriver for Baremetal testing

This virtual_power_driver provides the ability for baremetal driver to
start/stop/reboot VMs within common dev/test environments. Its goal is to
approximate the same functionality as other PowerDrivers (eg. IPMI) within
a desktop development environments and within the devstack-gate environment.

Authored-by: Chris Krelle <nobodycam@gmail.com>
Co-authored-by: Devananda van der Veen <devananda.vdv@gmail.com>

Change-Id: I9935a9a30a166a9c28a9abb139c49f219a32ddd7
Merge "Add a virtual PowerDriver for Baremetal testing"