Add watchdog device support to libvirt driver

This commit adds support for watchdog devices
to the libvirt driver.  The watchdog device
used is 'i6300esb', and the action is based
or the 'hw_watchdog_action' property of the image.

Implements: blueprint libvirt-watchdog
DocImpact

Change-Id: Icf1f51d7929e40d0caeae569bd2b6eee8be9689e
Merge "Add watchdog device support to libvirt driver"