lb agent should not only check if the device exists but also if it´s up

[Rossella Sblendido]

Lb agent before creating a bridge checks if it already exists. If it exists, it doesn´t creates a new one. Anyway if the device exists but it´s not up, the agent doesn´t set it up.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/76309

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/76309
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=546a38fca6b5e9c389074c2365bf15b1071575ef
Submitter: Jenkins
Branch: master

commit 546a38fca6b5e9c389074c2365bf15b1071575ef
Author: rossella <email address hidden>
Date: Fri Apr 4 13:13:31 2014 +0000

    Check if bridge exists and make sure it's UP in ensure_bridge

    Introduce _bridge_exists_and_ensure_up that checks if the bridge
    exists and if it's DOWN sets it UP

    Change-Id: Ide9d2bb04016cadb347b00cadbee7007e61bd01e
    Closes-bug: #1282741