Fix validate failed with a image_name in uuid format

[huangtianhua]

1. stack-create with an image name in uuid format:

    heat stack-create -f hello_world.yaml -P ImageId=751822b9-5f30-48af-992a-67c9faeacaaa stack3

2. validate failed:
    ERROR: Property error : my_instance: image "751822b9-5f30-48af-992a-67c9faeacaaa" does not validate glance.image

3. according to the "constraints.CustomConstraint('glance.image') ", heat will check whether the image is exist, but the check in not correct when the name in uuid format.

[Openstack Gerrit (openstack-gerrit)]

Fix proposed to branch: master
Review: https://review.openstack.org/90295

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/90295
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=9b1e2b1f5dfa61b9d9bfbcb272faf0512fa0c08d
Submitter: Jenkins
Branch: master

commit 9b1e2b1f5dfa61b9d9bfbcb272faf0512fa0c08d
Author: huangtianhua <email address hidden>
Date: Fri Apr 25 14:50:27 2014 +0800

    Fix validate failed with an image_name in uuid format

    We should support to get the image_id by an image_name which is in uuid
    format.

    Change-Id: I471ee57ea55f990f852398a43762899dbc3d8692
    Closes-Bug: #1312523