Shelve_offload should support clean_shutdown

[Phil Day]

Change https://review.openstack.org/#/c/112988/ added clean_shutdown support for shelve(), but instances booted from volumes are shelved via shelve_offload() - so that should also support clean_shutdown

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/130548

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/130548
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=c79fb64c1f287501930af6709902dbd99942e406
Submitter: Jenkins
Branch: master

commit c79fb64c1f287501930af6709902dbd99942e406
Author: Phil Day <email address hidden>
Date: Thu Oct 23 14:11:29 2014 +0000

    Shelve_offload() should give guests a chance to shutdown

    Change Iec3dfd17725440958aac395ebc471e51afd6522e added clean_shutdown
    support to shelve operations, but ignored shelve_offload as its normally called
    either as a second stage to shelve(). However BFV instances call
    shelve_offload() directly, so it too should have clean_shutdown support.

    Change-Id: Ida612a70ad3b8a7b7b9454579870569c4129ee48
    Closes-Bug: 1384637
    Partially-Implements: blueprint user-defined-shutdown