Comment 9 for bug 1573073

Reviewed: https://review.openstack.org/393739
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=5a3dadc60103a8c2dc88446fe4b2412c9bdf0790
Submitter: Jenkins
Branch: stable/newton

commit 5a3dadc60103a8c2dc88446fe4b2412c9bdf0790
Author: Saverio Proto <email address hidden>
Date: Thu Apr 21 16:50:07 2016 +0200

    Check if namespace exists before getting devices

    If a neutron router has no ports defined, its namespace is deleted
    by the cronjob /etc/cron.d/neutron-l3-agent-netns-cleanup.
    It is required to check if the namespace exists before calling
    iproute2 commands against the namespace.
    It is not enough for the string of the namespace uuid to be defined,
    the namespace must really exist on the network node.
    This patch checks if the namespace exists when calling get_devices().
    Otherwise the agent log file will be flooded with messages like
    Cannot open network namespace "qrouter-<uuid>": No such file or directory
    Failed to process compatible router '<uuid>'

    Related-bug: 1573073

    Change-Id: I744ef11529f9da5cbfdb812de0b35b95f9d078bb
    (cherry picked from commit 7675495f260daf0174f4e04b36279513889df19a)