Comment 4 for bug 1888680

This is a deficiency in the NFS driver w.r.t. encrypted volumes, to fix it we should implement a driver copy_image_to_encrypted_volume() method to handle this path. Without it, NFS is currently falling into the base driver generic copy_image_to_encrypted_volume() method which does not work for how NFS managed encrypted volumes.

This method for the NFS driver should mirror how the RBD driver's copy_image_to_encrypted_volume works:
- download the image to a temp file
- call something similar to the RBD driver's _encrypt_image() method which calls image_utils.convert_image() etc to encrypt the image and copy it into the volume file.