audit middleware incorrectly stores event in object

[gordon chung]

in audit middleware, we store the cadf event between request and response to utilise the same event. currently it is incorrectly stored as an object variable of the middleware so it's possible that a subsequent request could end up using the event from a previous request.

we need to change this and store the event so that it's scoped to the request. this can be done by storing event in request itself.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/149300

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/149300
Committed: https://git.openstack.org/cgit/openstack/keystonemiddleware/commit/?id=5839e7c75888e08283976eca95d6ded1a979573b
Submitter: Jenkins
Branch: master

commit 5839e7c75888e08283976eca95d6ded1a979573b
Author: gordon chung <email address hidden>
Date: Thu Jan 22 09:55:07 2015 -0500

    make audit event scoped to request session and not middleware

    this patch scopes the built audit event to the request rather than
    incorrectly scoping it to the middleware.

    Change-Id: I41d0deaa450191c5eb18de12a1bd26a26ceeebe5
    Closes-Bug: #1413617