wrong description when updating quotas

[Lingxian Kong]

when updating quota for a resource, with 'force_update=false', an exception will be raised when the new value is less than the used quota values(used and reserved), but the exception information is not correct, which should be fixed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/53062

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/53062
Committed: http://github.com/openstack/nova/commit/65df7336994b03b12aecf9bcdafcfb0d839815f9
Submitter: Jenkins
Branch: master

commit 65df7336994b03b12aecf9bcdafcfb0d839815f9
Author: LingxianKong <email address hidden>
Date: Tue Oct 22 14:45:32 2013 +0800

    Fix wrong description when updating quotas

    when updating quota for a resource, with 'force_update=false', an
    exception will be raised when the new value is less than the used quota
    values(used and reserved). This patch changes the description of
    exception.

    Change-Id: Iede70444341817afb6953eb604fe4de186622916
    Closes-bug: #1243062