Comment 4 for bug 1744383

Reviewed: https://review.openstack.org/536529
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=0e57f89b8b0e3ed39c7fe59ee9b4e5cf3b8711b6
Submitter: Zuul
Branch: stable/pike

commit 0e57f89b8b0e3ed39c7fe59ee9b4e5cf3b8711b6
Author: Mohammed Naser <email address hidden>
Date: Fri Jan 19 11:45:41 2018 -0800

    Move disk space check to run when needed

    At the moment, the check for disk space when booting from an image
    currently happens regardless if the backend supports cloning or not.

    This means that even if a backend can clone the image directly, the
    control plane must have enough disk to download the entire image
    which can be unreasonable in backend such as RBD.

    This patch moves the code which checks for enough disk space to be
    in the same function that effectively downloads the image, ensuring
    that it only runs when an image has to be downloaded and avoiding
    the check if the backend successfully cloned the image.

    Closes-Bug: #1744383
    Change-Id: Ibfd6f40e8b8ab88d4ec76e9ac27617a0f97b6c29
    (cherry picked from commit f62f8abad17d1c287d48ea273ea4c4fe7f536d07)