functional readonly_cli tests pass with incorrect input

[Anton Arefiev]

Functional readonly_cli tests checks resources attribute for diff cinder cmds, the problem is that they are always false positive.

The root cause of the problem is parser.listing method return empty list if env doesn't have resources, so assertTableStruct always passes.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/185660

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/185660
Committed: https://git.openstack.org/cgit/openstack/python-cinderclient/commit/?id=d547d2779aab59a100eed0d0c15b4b4b85d37b59
Submitter: Jenkins
Branch: master

commit d547d2779aab59a100eed0d0c15b4b4b85d37b59
Author: Anton Arefiev <email address hidden>
Date: Tue May 26 19:22:32 2015 +0300

    Fix functional readonly_cli tests

    Parser.listing method return empty list if env doesn't have resources,
    so assertTableStruct works wrong, doesn't check field names in the
    output table.

    This change add new assert(assertTableHeaders) to check resource
    attributes.

    Change-Id: Ieca67b5cc2202467527c5a2dfbd7b2f2b4d5ad8d
    Closes-Bug: #1458932