import_class() does not report original exception

[Kevin L. Mitchell]

Glance has a copy of the nova import_class() utility function, and has this same problem. Nova bug 820642, original description:

The utils.import_class() function does a very handy thing, but it catches ImportError and simply raises a NotFound exception without including in the message what the original error was. This caused a problem when glance added xattr to its requirements, in that all we get is this mysterious message that "Client could not be found". It wouldn't take much to augment the "NotFound" message with the text of the original exception, which could give us a better clue as to how to fix the problem.

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/825
Committed: http://github.com/openstack/glance/commit/53db059772d8c89facd17970fc967ef2fa1866c5
Submitter: Jenkins
Branch: master

 status fixcommitted
 done

commit 53db059772d8c89facd17970fc967ef2fa1866c5
Author: Jay Pipes <email address hidden>
Date: Mon Oct 10 13:44:22 2011 -0400

    Refactoring/cleanup around our exception handling

    Fixes LP Bug #820643 - import_class() does not
    report original exception.

    * Makes ALL exceptions now use base exception class
    * Removes unused exception classes from Nova
    * Removes unused code in glance.common.utils
    * Adds unit tests for bool_from_string and import_class

    Change-Id: If6775eb3ce85390bc5d579dff6c59c6066e77e9b