NetApp implementation for copy offload in clustered nfs driver

The Copy offload binary is a special RPC implemented in Ontap that
allows NFS clients to ask the server to copy data between
volumes in the same cluster efficiently. The special
binary will be developed by NetApp and distributed to its customers.
It will address two copy cases after efficient image clone failed.
First when image cache file is present in a different share than
the one holding volume. Second when glance is backed by nfs share
which is on the same cluster as nfs driver backend. Instead
of regular http download the copy offload workflow will be used to copy
image to share and volume. Resubmitting it as there was a problem
with build in previous submission.

Change-Id: I0847d47cecdec8be2ade06d0ea944cc3fa6f476b
Implements: blueprint copyoffload