Nova api doesn't handle InstanceUnknownCell when doing live-migration

[Eli Qiao]

compute_api.live_migrate may raise InstanceUnknownCell exception when doing check_instance_cell.
see https://github.com/openstack/nova/blob/master/nova/compute/api.py#L316 for reference.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/212965

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/212965
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=cbcf5932be3d65b77bed92c70e32579a13b9115f
Submitter: Jenkins
Branch: master

commit cbcf5932be3d65b77bed92c70e32579a13b9115f
Author: Eli Qiao <email address hidden>
Date: Fri Aug 14 11:56:00 2015 +0800

    API: Handle InstanceUnknownCell exceptions

    There are some methods in Nova compute api and cell api would call the
    decorator `check_instance_cell`, and that decorator may raise
    InstanceUnknownCell, there isn't any exception handler in REST api layer.

    This patch adds handlers for those methods.

    Closes-bug: #1484776
    Change-Id: I753a81f093ec5fdf000841949e52fca6f2662aa8