Preserve traceback in re-raised exception in Cisco plugin

[Paul Michali]

Improve the handling of re-raised exceptions to preserve the traceback information in the Cisco plugin, as needed.

In particular, in cisco_nexus_network_driver_v2.py nxos_connect() may re-raise an exception under a different type, but will loose the T/B info for the original exception. Determine if the T/B should be propagated, or left.

Analyze other cases where exceptions are rethrown to see if they need the
T/B preserved.

[Paul Michali (pcm)]

After analyzing the code, altered the description to better reflect the goals of the bug.

For the case mentioned, and for some of the cases where database exceptions are re-thrown, we don't need to preserve the T/B, IMHO. However, there are other cases where the exception processing code can be cleaned up.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/43508

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/43508
Committed: http://github.com/openstack/neutron/commit/cf1af8d282cd549ff554c7e1f5663cd3999d843e
Submitter: Jenkins
Branch: master

commit cf1af8d282cd549ff554c7e1f5663cd3999d843e
Author: Paul Michali <email address hidden>
Date: Fri Aug 23 11:47:24 2013 -0400

    Analyze re-raised exceptions in Cisco Plugin

    Checked all cases of re-raised exceptions. In several cases, the exception
    was redundant (re-raising the same exception), so the try block and
    exception handling was removed.

    In one case, exceptions raised from two sources were re-raised with a
    a different exception. Instead of doing this, the original exceptions
    were changed and the try block and re-raised exception were removed.

    In cases where there were database exceptions that were re-raised as
    Neutron exceptions, the traceback was left as-is, since it was more
    informative to know the higher level source of the issue.

    The same was true for the exception mentioned in the bug, where the
    original failure was in the ncclient library parsing the configuration
    and it would be more descriptive to know that there was a connection
    failure or a config failure, that to know the library method.

    bug 1213159

    Change-Id: Ie334d2548bf651c61e878bf797adaf8c5880eb86