Comment 18 for bug 1557909

Reviewed: https://review.openstack.org/351923
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=6e5892da1434a1a7674456aa4c897480fbb0208b
Submitter: Jenkins
Branch: stable/mitaka

commit 6e5892da1434a1a7674456aa4c897480fbb0208b
Author: Swaminathan Vasudevan <email address hidden>
Date: Tue Jun 7 13:31:56 2016 -0700

    DVR: Clean stale snat-ns by checking its existence when agent restarts

    At present there is no clear way to distinguish when the snat_namespace
    object is initialized and when the actual namespace is created.
    There is no way to check if the namespace already existed. The
    code was only checking at the snat_namespace object instead of its
    existence.

    This patch addresses the issue by adding in an exists method to the
    namespace object to identify the existence of the namespace in the
    given agent.

    This would allow us to check for the existence of the namespace,
    and also allow us to identify the stale snat namespace and
    delete the namespace when the gateway is cleared as the agent restarts.

    This also applies for conditions when the router is manually moved
    from one agent to another agent while the agent is dead. When the
    agent wakes up it would clean up the stale snat namespace.
    Change-Id: Icb00297208813436c2a9e9a003275462293ad643
    Closes-Bug: #1557909
    (cherry picked from commit acd04d668bd414cd21f2715adc6a35a0eaed59a3)