Fix for the bug 1400966 prevents user from specifying image nfs
share location as location value for an image.
This broke Tintri's image direct clone feature.
This addresses the issue by using provider_location of image
metadata to specify image nfs share location.
DocImpact
Closes-Bug: #1528969
Co-Authored-By: opencompute xuchenx@gmail.com
Change-Id: Icdf2f229d79d5631604e87dd9dd30a1608e6b010