LBaaS V2 Octavia driver should create get its own context/session

[Brandon Logan]

The LBaaS V2 Octavia driver currently uses the context that is passed from the plugin. Since the driver spins up a thread to poll Octavia, each thread should create its own context.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/225542

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/225542
Committed: https://git.openstack.org/cgit/openstack/neutron-lbaas/commit/?id=a3a3531aff2bd830d740fd8418011eaa3dc4a831
Submitter: Jenkins
Branch: master

commit a3a3531aff2bd830d740fd8418011eaa3dc4a831
Author: Brandon Logan <email address hidden>
Date: Sun Sep 20 22:41:16 2015 -0500

    Use admin context in octavia driver, improve logs

    When polling for the status of a load balancer in octavia, the context created
    by the plugin was being used. Since the polling takes place in a thread, that
    context can have some unexpected behavior. It is better to create an admin
    context in the thread because it definitely exists in that thread.

    Also improve debug logging in the octavia driver and the successful and failed
    completion helper methods in the mixins.

    Change-Id: I6f64c95d89876c9d1d19076a4fe7e3006a0df5e0
    Closes-Bug: #1497823