VMware: virt unrescue method now supports objects

Commit 65ad230af5ece020822fa963dd30fd641a54ae91 ensured
that the compute API and manager are now getting objects
for the unrescue method.

This patch adds support to the virt driver code.

Change-Id: I42fa532d5b2b1c92121216ac31b56a7b595d59e7
VM diagnostics: add serializer to Diagnostics object

The serializer will enable the API to return a dictionary to the
user.

Part of the blueprint v3-diagnostics

Change-Id: If86a94cba98745acbc9976fa7354c98ec6716ac0
Merge "VM diagnostics: add serializer to Diagnostics object"
Merge "VMware: virt unrescue method now supports objects"