Add unit tests for glance.api.cached_images module

[Tatyanka]

OpenStack glance.api.cached_images module is not covered by unit tests.
Would be nice to minimize uncovered parts of code as possible.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/24447

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/24447
Committed: http://github.com/openstack/glance/commit/715513404b491b721dd0906d4c6f0ef7b1805294
Submitter: Jenkins
Branch: master

commit 715513404b491b721dd0906d4c6f0ef7b1805294
Author: Tatyana Leontovich <email address hidden>
Date: Thu Mar 14 17:39:34 2013 +0200

    Add unit tests for glance.api.cached_images module

    Add positive unit tests for methods:
    * get_chached_images
    * delete_cached_images
    * get_queued_images
    * queue_image
    * delete_queued_image

    Fixes: bug #1155188
    Change-Id: I3fa6dc28a72e8c6e8402911931fb37e18cba7ea0