Fixes create rbd volume from image v1 glance api

The RBD driver supports two methods of image cloning;
thin copy i.e. copy-on-write (requires v2 Glance API)
and full copy (default if v2 Glance API is not available).

clone_image() was failing in the Glance V1 API case because
it was not returning a tuple, as expected by the volume
manager. Glance V2 support works fine.

Fixes: bug #1208617

Change-Id: I2e8605eaacfe8b65bdf47cb6ea40ef62d6f6b895
Merge "Fixes create rbd volume from image v1 glance api"