CredentialNotFound exception is referenced but not defined

Fix proposed to branch: master
Review: https://review.openstack.org/24575

Reviewed: https://review.openstack.org/24575
Committed: http://github.com/openstack/keystone/commit/90fcb996cb2acf7b829b2cccfa485c09e4c0d0e8
Submitter: Jenkins
Branch: master

commit 90fcb996cb2acf7b829b2cccfa485c09e4c0d0e8
Author: Henry Nash <email address hidden>
Date: Fri Mar 15 22:48:50 2013 +0000

    Ensure delete domain removes all owned entities

    Deleting a domain should delete all Users, Groups and Projects
    that are owned by that domain. This is intertwined with making sure
    that deleting Users/Projects clean up their relevant Tokens and
    Credentials (raised as a separate bug, bug fixed here).

    To help avoid inadvertent deletion, we insist that a domain must
    be disabled before it can be deleted.

    In implementing this change, it was discovered that the exception
    CredentialNotFound is referenced in the identity backend, but
    never defined - this was needed here for the unit tests. This is raised
    as a separate bug, and fixed here. A further bug has been raised
    that this indicates we are lacking in negative testing for
    Credentials (not fixed in this change)

    Fixes Bug #1097995
    Fixes Bug #1155921
    Fixes Bug #1155924

    Change-Id: Ibc926f8212fb9bd4426088339a21002a07c86984