As well as PublishReturned and ConnectionException, messaging
can raise PublishTimeout (publishing timed out) or
PublishForbidden (publishing was denied for lack of permission)
when you attempt to publish a message. We should handle these
as well. At present it seems like if this happens, the exception
being unhandled ultimately causes WSGI to return a 500 or 504
error to the client that submitted the result; the client may
then try and submit the result again, leading to it being
duplicated many times. If we handle the exception instead, the
client should get a successful response and not re-submit the
result. The message not being published is still a problem, but
probably not as bad as clients constantly re-submitted results
forever.

Signed-off-by: Adam Williamson awilliam@redhat.com