xenapi: migrate does not work with volume backed instance

[Andrew Laski]

If the migrate action is requested on a volume backed instance using the xenapi driver the action will fail when it tries to snapshot the root disk. The migrate process assumes an image backed instance currently.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/124906

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/124906
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a234e16ca68b9dd63f6132cfdfc9faa6fc427e25
Submitter: Jenkins
Branch: master

commit a234e16ca68b9dd63f6132cfdfc9faa6fc427e25
Author: Andrew Laski <email address hidden>
Date: Mon Sep 29 18:04:08 2014 -0400

    Xenapi: Allow volume backed instances to migrate

    The migrate process had no provisions for a non image backed instance.
    This remedies that by doing a few things:

    Don't snapshot the root disk on the source host.
    Don't try to import the root disk on the destination host.
    Connect the volume to the destination host as the boot device.

    Change-Id: Ia453cf33a36803b1b5447c6240988a3dd603f328
    Closes-bug: #1375480