Fix return/generation of the x-openstack-request-id header

[John Vrbanac]

As a user, if you include the x-openstack-request-id header on a request it doesn't get returned back to the user on the response for proper request tracking. Instead it just logs a warning saying "Unable to retrieve request id from context". This functionality should return the request id provided by the user or generate one if the request id wasn't provided.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/158034
Committed: https://git.openstack.org/cgit/openstack/barbican/commit/?id=ce8d9fd39dac16b9b53a9c1192613d3b93ffd9ee
Submitter: Jenkins
Branch: master

commit ce8d9fd39dac16b9b53a9c1192613d3b93ffd9ee
Author: John Vrbanac <email address hidden>
Date: Fri Feb 20 23:46:12 2015 -0600

    Fixing unable to retrieve req id bug

    Properly returning the id if it was provided on the request. If not,
    generate an id in the format expected by openstack services
    and clients.

    Context:
    The original code in BaseContextMiddleware was copied from Glance
    at the beginning of the project, but it has never worked because
    we don't build our requests and responses like Glance does. As
    a result, the old code has been logging a "Unabled to retrieve request
    id from context" warning for every response. This change properly
    retrieves the id (if there), or generates one if needed.

    Closes-Bug: 1424221
    Change-Id: I7e22474775de3c3f33968144d098bedbfc462e7a