Improve rpc RemoteError to return original exception args

[Dean Troyer]

The original exception information returned in an rpc.RemoteError is reduced to strings. We need a way to return the original exception args intact to the calling routines.

[Brian Waldon (bcwaldon)]

Being able to return enough information to reconstruct the same exception on the other side of an rpc connection would be fantastic.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/5749

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/5749
Committed: http://github.com/openstack/nova/commit/a0150a4d9e751ec222221558dfe89a66b0c118ab
Submitter: Jenkins
Branch: master

commit a0150a4d9e751ec222221558dfe89a66b0c118ab
Author: Alex Meade <email address hidden>
Date: Wed Mar 21 19:13:16 2012 +0000

    Add the serialization of exceptions for RPC calls.

    This change uses json to serialize an exception so that it can be sent
    through RPC calls to be reconstructed on the other side. The traceback is added
    to the exception message. If recreating the exception fails for whatever reason
    then a RemoteError is created containing all of the exception information.

    Adds flag 'allowed_rpc_exception_modules' to prevent dangerous modules from
    being accessed and allowing arbitrary code to be run.

    Fixes bug 920705
    Fixes bug 940500

    Change-Id: Ife3b64b19fe8abbc730184d4ee7d9fcabfd29db3