Comment 17 for bug 1301374

Julie, I've tried to as explanatory as I could in the commit message, but perhaps the above picture could explain the things better. It is produced for the Neutron service being shut down just before pressing the final 'Create' button at the 'CreateNetwork' workflow. Here you see 2 error messages generated for the `CreateNetwork` workflow which has `show_multiple_failures` set to `False`. The reason there are 2 messages is that they are generated for different request-response cycles: the first long message gets into request before this line https://github.com/openstack/horizon/blob/2014.2.1/horizon/workflows/views.py#L195 is executed, while the second is added right after the redirect. If I clear messages just before `exceptions.handle(request)` line, there won't be any specific message about the cause of the unexpected error (which is not recoverable).

So I propose to reduce the number of messages only for recoverable (expected) errors, because it's not clear to which error message we should reduce a bunch of them in case they were caused by some unexpected failure.