Avoid copying task detail users tasks results

[Joshua Harlow]

It is unsafe to copy users tasks results (since we can not guarnatee they are copyable, even using copy.copy which does a shallow copy); this causes issues like the following with sqlalchemy results:

'''2015-05-07 22:42:51.142 17040 TRACE oslo_messaging.rpc.dispatcher ObjectDereferencedError: Can't emit change event for attribute 'Volume.provider_location' - parent object of type <Volume> has been garbage collected.'''

'Exception during message handling: Can't emit change event for attribute 'Volume.provider_location' - parent object of type <Volume> has been garbage collected.'''

[Joshua Harlow (harlowja)]

http://lists.openstack.org/pipermail/openstack-dev/2015-May/063642.html with more context/info.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/181288
Committed: https://git.openstack.org/cgit/openstack/taskflow/commit/?id=e6a04193e73bd44450eca9859b035cf91b4fcf4b
Submitter: Jenkins
Branch: master

commit e6a04193e73bd44450eca9859b035cf91b4fcf4b
Author: Joshua Harlow <email address hidden>
Date: Thu May 7 20:49:46 2015 -0700

    Avoid trying to copy tasks results when cloning/copying

    It is not always safe to copy task results so instad of
    trying to copy.copy them just retain the existing results
    in the clone (and avoid copying any users results if
    they exist).

    This appeared to be causing sqlalchemy weak references to
    get garbage collected prematurely in cinder.

    Fixes bug 1452978

    Change-Id: I75e4ad0e9eb50284ff09179565b6d146a8da3d92