root_helper is defined inconsistently defined in config files

[Mark McClain]

The root_helper config option is defined in both [DEFAULT] and [AGENT] configuration groups in various agents throughout the code base. The location should be standardized into one configuration group: [AGENT].

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/20603

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/20603
Committed: http://github.com/openstack/quantum/commit/1b7565b83ca8ef9761cdfb1eed1e9eb9498ea340
Submitter: Jenkins
Branch: master

commit 1b7565b83ca8ef9761cdfb1eed1e9eb9498ea340
Author: Gary Kotton <email address hidden>
Date: Mon Jan 28 13:37:47 2013 +0000

    Define root_helper variable under the [AGENT] section

    Fixes bug 1105523

    The patch set adds 2 new functions:
    1. register_root_helper - this enables all wanting to use
    the root_helper variable. This is under the section AGENT.
    2. get_root_helper - this is a helper function that returns the
    root_helper. This should be used when the application used to
    have the root_helper defined under the section DEFAULT. This
    ensures backward compatability.

    Change-Id: Iba72c4fc89ba5329ea045483287012f82b306250