Comment 2 for bug 1311971

Reviewed: https://review.openstack.org/90300
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=4539ff26d903174c844d6571533dfe719195e107
Submitter: Jenkins
Branch: master

commit 4539ff26d903174c844d6571533dfe719195e107
Author: Li Ma <email address hidden>
Date: Fri Apr 25 00:37:46 2014 -0700

    Database exception causes UnboundLocalError in linuxbridge-agent

    When database exception raises from update_device_down,
    the linuxbridge-agent doesn't deal with them in a proper way
    that causes accessing not-existed local variables.

    A straightforward workaround is to set it as None by default
    and verify its value then.

    Change-Id: I32a9467876a619a7d0ad53ff3d5d95ff977e54f4
    Closes-Bug: #1311971