Unit test case for unshelving a volume backed instance is not correct

[Xiaowei Qian]

In case of volume backed instance, snapshot is not taken when an instance is shelved,
so "shelved_image_id" key is not set to the instance system metadata.

In the unit test case "test_unshelve_instance_schedule_and_rebuild_volume_backed
", set the "shelved_image_id" to the instance system metadata, which is not correct.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/213633

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/213633
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=5e821e364429153ba3685489ff2281966ce8496e
Submitter: Jenkins
Branch: master

commit 5e821e364429153ba3685489ff2281966ce8496e
Author: Xiaowei Qian <email address hidden>
Date: Wed Sep 16 10:35:33 2015 +0800

    Remove "shelved_image_id" key from instance system metadata

    In the unit test case "test_unshelve_instance_schedule_and_rebuild_volume_backed
    ", set the "shelved_image_id" to the instance system metadata,
    it tests the instance boot from image, not boot from volume.
    So it needs to remove "shelved_image_id" from the metadata,
    and remove "image_api.get" mock method.

    Change-Id: Ie501acaaa1c961a4b6f1f4ea9726a5b11b0de709
    Closes-Bug: #1485429
    Signed-off-by: Xiaowei Qian <email address hidden>