Libvirt-LXC can leave image mounted to host

[Rick Harris]

If an error occurs creating a Libvirt+LXC domain, the code can leave the guest FS mounted to host preventing the `lvremove` of a delete from working.

The core problem here is that any code between `setup_container` and `teardown_container` needs be within a `try/finally` block, so that on error, we unmount the image from the host.

While we're at it, we can also cleanup the exception handling by reducing the 3 independent exception handlers into a single one, which is then followed by the `finally` clause.

[Rick Harris (rconradharris)]

Just FYI, proposed this patch a while back: https://review.openstack.org/#/c/102324/

[Vladik Romanovsky (vladik-romanovsky)]

OK. Usually, bugs are being assigned to the person who pushed the patch and change the status..

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/102324
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=60c90f73261efb8c73ecc02152307c81265cab13
Submitter: Jenkins
Branch: master

commit 60c90f73261efb8c73ecc02152307c81265cab13
Author: Rick Harris <email address hidden>
Date: Tue Jun 24 14:03:17 2014 -0500

    libvirt+lxc: Unmount guest FS from host on error

    If an error occurs during `_create_domain`, we need to ensure that the guest's
    FS is unmounted from the host in all cases.

    This is necessary because, if we leave the FS mounted to the host, the
    `lvremove` triggered by `delete` won't work because the filesystem will
    'still be in use'.

    The solution is to wrap the code in a `try/finally` to ensure the cleanup
    routines (which unmount) are always called.

    Change-Id: If863cf813dddc1e4554fb87b945c68b75b25f9a2
    Closes-Bug: 1333827