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
VMware: DatastorePath join() and __eq__()

There are quite a number of use cases where we construct additional
datastore paths out of one representing some ancestor directory,
so implemented a join() method that allows for just that.
It is useful to define equality operator when comparing two DatstorePath
objects, so added that as well.

partial blueprint vmware-spawn-refactor
Change-Id: Iec44fdd0beba232b57bcd0a07c39e628208ca9b2
Merge "VMware: DatastorePath join() and __eq__()"
Merge "xenapi: virt rescue method now supports objects"