libvirt: virt rescue method now supports objects

Commit a37a96fd13b933123e80ad24e37fc37d73c16059 ensured
that the compute API and manager are now getting objects
for the rescue method.

This patch adds support to the virt driver code.

Change-Id: I2ae89f937b1983a2b0599e2eded343aa8358dbba
Merge "libvirt: virt rescue method now supports objects"