nova cell showing should raise more information on v2 API

[ugvddm]

nova cell showing should raise more information on v2 API, instead of "The resource could not be found. "

[Openstack Gerrit (openstack-gerrit)]

Fix proposed to branch: master
Review: https://review.openstack.org/92586

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/92586
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=2ddc905ebba6e6b2bd5be2ca45a14115ef5a6e8f
Submitter: Jenkins
Branch: master

commit 2ddc905ebba6e6b2bd5be2ca45a14115ef5a6e8f
Author: Zhengguang <email address hidden>
Date: Tue May 6 10:17:42 2014 -0400

    Fix the explanation of HTTPNotFound for cell showing v2 API

    This patch adds the explanation to cell showing in v2 API, when
    the cell is not found, the exception of HTTPNotFound will return
    more infomation.

    Change-Id: I25dee08a04ad974af5309999527e0f173d2c2cab
    Closes-Bug: #1316152