Comment 3 for bug 1462024

Reviewed: https://review.openstack.org/224293
Committed: https://git.openstack.org/cgit/stackforge/group-based-policy/commit/?id=7acac86b65f360b1b0dc230cc944c96f1366d9dd
Submitter: Jenkins
Branch: master

commit 7acac86b65f360b1b0dc230cc944c96f1366d9dd
Author: Robert Kukura <email address hidden>
Date: Wed Sep 16 14:50:26 2015 -0400

    Handle concurrent implicit L3P creation

    In the implicit_policy driver, when creating a default L3 policy,
    raise DefaultL3PolicyAlreadyExists if an L3 policy named 'default'
    already exists.

    If DefaultL3PolicyAlreadyExists is raised when the implicit_policy
    driver attempts to create the default L3 policy for a tenant, query
    again to see if a default L3 policy has been concurrently created, and
    if so, use that. This requires adding local_api wrappers for
    postcommit group policy resource CRUD operations called in the
    implicit_policy driver, so that clean DB sessions are used.

    Also, fix the resource_mapping driver's
    delete_policy_target_group_postcommit to gracefully handle partially
    constructed states, such as a null L2 policy or a subnet not attached
    to a router.

    Closes-bug: 1462024
    Partial-bug: 1417312

    Change-Id: I09f29eef22edb45290070aae30e97c93c77ea341