ZeroMQ driver options are current stored into the DEFAULT group.
This change makes the zmq configuration clearer by putting its
options into oslo_messaging_zmq group.
Change-Id: Ia00fda005b1664750d2646f8c82ebdf295b156fb
Closes-bug: #1417040
Co-Authored-By: Oleksii Zamiatin <ozamiatin@mirantis.com>