Comment 20 for bug 1374473

Reviewed: https://review.openstack.org/195223
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=884013c8cdfe97d297103b0feada849ecad7c113
Submitter: Jenkins
Branch: stable/juno

commit 884013c8cdfe97d297103b0feada849ecad7c113
Author: Swaminathan Vasudevan <email address hidden>
Date: Wed Dec 17 17:15:07 2014 -0800

    Fixes Multiple External Networks issue with DVR

    Current L3 agents can support more than one
    external network when configured properly.

    On DVR routers, router-gateway-set was
    returning a 500 error, when two external
    networks were configured in the system.

    The problem resides in the scheduler where the
    bind_router is called twice when the
    reschedule_router is called from update_router.

    The _schedule_router binds the snat
    and the qrouter with the respective agents.

    But after scheduling it does not return agent.

    And in the case of two external networks, the
    get_candidates always returns a valid candidate
    to be processed and hence the bind_router is
    called twice.

    This patch fixes the _schedule_router function
    and hence avoids the multiple calls to
    bind_router.

    This prevents the update_router from failing
    and causing the nested rollback for the
    transactions.

    Conflicts:
            neutron/tests/unit/test_l3_schedulers.py

    (cherry picked from commit 3794b4a83e68041e24b715135f0ccf09a5631178)
    Change-Id: I24d44c60a3ea5bbc9e3f44aa5191deff315723ca
    Closes-Bug: #1374473