assignment driver config option missing

[Brant Knudson]

Keystone's sample config file doesn't include the assignment.driver option.

 [assignment]
 # driver =

It's referenced in assignment.Manager:

 assignment_driver = CONF.assignment.driver

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/37739

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/37739
Committed: http://github.com/openstack/keystone/commit/eca1ca35fcf9ceec071a1b550ae7faf9c1a4db98
Submitter: Jenkins
Branch: master

commit eca1ca35fcf9ceec071a1b550ae7faf9c1a4db98
Author: Brant Knudson <email address hidden>
Date: Thu Jul 18 13:22:09 2013 -0500

    Add [assignment].driver to sample config

    There's a new config option [assignment].driver that wasn't included
    in the sample config file. This makes it more difficult than necessary
    for deployers to configure.

    Fixes bug 1202778

    Change-Id: I04b09c214b9ea997d8f540a72978ce9b19b4138d