Allow users to see what resources will be changed during a stack-update.
Docs change here https://review.openstack.org/132870/
Client change here https://review.openstack.org/#/c/126957/
BP: update-dry-run
Co-Authored-By: Jason Dunsmore <jasondunsmore@gmail.com>
Change-Id: If58bdcccfef6f5d36c0367c5267f95014232015e