VMware: fix rescue disk location when image is not linked clone

A rescue of a VM that has an image which is not linked clone would
create the rescue disk in the original VM's folder and not in the
rescue VM's folder. When the unrescue takes place the rescue disk
will not be deleted.

The patch adds unit tests that validates that the rescue disk location
is correct.

Change-Id: I17dfcade0a162057219bc6d108987bec53f526f9
Co-authored-by: Vui Lam<vui@vmware.com>
Closes-bug: #1293435
Merge "VMware: fix rescue disk location when image is not linked clone"