Libvirt-lxc will leak nbd devices on instance shutdown

[Andrew Melton]

Shutting down a libvirt-lxc based instance will leak the nbd device. This happens because _teardown_container will only be called when libvirt domain's are running. During a shutdown, the domain is not running at the time of the destroy. Thus, _teardown_container is never called and the nbd device is never disconnected.

Steps to reproduce:
1) Create devstack using local.conf: https://gist.github.com/ramielrowe/6ae233dc2c2cd479498a
2) Create an instance
3) Perform ps ax |grep nbd on devstack host. Observe connected nbd device
4) Shutdown instance
5) Perform ps ax |grep nbd on devstack host. Observe connected nbd device
6) Delete instance
7) Perform ps ax |grep nbd on devstack host. Observe connected nbd device

Nova has now leaked the nbd device.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/120196

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/120196
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=5f93c841a80663b68da2fb04df78d5acd0754d68
Submitter: Jenkins
Branch: master

commit 5f93c841a80663b68da2fb04df78d5acd0754d68
Author: Andrew Melton <email address hidden>
Date: Tue Sep 9 15:29:28 2014 -0400

    Libvirt: Always teardown lxc container on destroy

    This fixes a bug where shutting down a libvirt-lxc based instance
    would leak its underlying nbd device. This was happening because
    _teardown_container would only get called if the domain was
    present. After this fix, _teardown_container will always get called
    on a destroy, which ensures the nbd device gets disconnected.

    Change-Id: I8d0044fd038fef80568c6c86e34719ef679aa890
    Closes-Bug: #1367363