UnsupportedVersion exception could be more friendly

[Armando Migliaccio]

If an endpoint does not support a specific RPC version, the following stacktrace can be observed on the callee side:

http://paste.openstack.org/show/85970/

However there is no stacktrace on the caller side in case of cast operations.

Granted one can look the RPC version history to get a sense of what's going on, but sometimes the code is not very educated (as in people forget to update the docstrings), and it takes one or more rounds to get to the bottom of the issue.

It would be nice if the exception captured the method in question, so that it's easier to debug what's going on.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/107240

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/107240
Committed: https://git.openstack.org/cgit/openstack/oslo.messaging/commit/?id=ed886236f6c80b4f9379c941398b589b46c6ca6d
Submitter: Jenkins
Branch: master

commit ed886236f6c80b4f9379c941398b589b46c6ca6d
Author: armando-migliaccio <email address hidden>
Date: Tue Jul 15 22:57:11 2014 -0700

    Track the attempted method when raising UnsupportedVersion

    This helps in circumstances where the only stacktrace visible
    is on the target side (e.g. due to cast or fanout operations)
    and without the method information is difficult to root cause
    what is going on.

    Change-Id: I070ecda4d56186fcda8e8bfc49bf723928998393
    Closes-bug: #1340277