Updated openstack/openstack
Project: openstack/python-novaclient  94a4c49de056f7fb768814c1fe819d3899082c27
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Print a useful message for unknown server errors

If a server error is returned that has an unknown code, novaclient will
end up printing something similar to:

ClientException: <attribute 'message' of 'exceptions.BaseException' objects>

Setting a message for ClientException will ensure that something more
useful than that is printed.

Change-Id: I43a2a33017f9a5c1b79d7fd8af4153e91d296f7b
Closes-bug: 1295293