pipeline config in api-paste should be more flexible

[Akihiro Motoki]

From the review of bug #1028075 "Enable Keystone authN for Quantum in devstack".
https://review.openstack.org/#/c/10269/

A way to choosing a pipeline (in api-paste.ini) needs to be more flexible.
Introducting nova's approach lets the application choose the appropriate pipeline depending on AUTH_STRATEGY.
By doing this, we would not need in the future to change devstack for each change in the Quantum pipelines.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/10330

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/10330
Committed: http://github.com/openstack/quantum/commit/ddcc951f08dc24c2fc605b45937a429c2c354e51
Submitter: Jenkins
Branch: master

commit ddcc951f08dc24c2fc605b45937a429c2c354e51
Author: Akihiro MOTOKI <email address hidden>
Date: Thu Jul 26 17:48:48 2012 +0900

    Make quantum pipeline configurable from quantum.conf.

    Fixes bug 1029313.

    The current api-paste.ini does not provide a way to choose a pipeline:
    there is no way to switching a pipeline between keystone-enabled and
    noauth pipelines without modifying the pipeline directly.

    This commit introduces 'auth_strategy' flag to quantum.conf and
    a pipeline used is determined depending on the flag. Supported values for
    this flag are 'keystone' (default) and 'noauth' at the moment.

    Change-Id: Ieafaf31eaaec2b02727ed5d3bd36c907e50aee5b