xenapi: 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: I06e5032526f791dfc0c523f2302d2edff5023f78
Merge "xenapi: virt rescue method now supports objects"