Message style is unused in zmq driver

[Mark McLoughlin]

As discussed here:

  https://review.openstack.org/#/c/13423/1/quantum/openstack/common/rpc/impl_zmq.py

The message style sent over the wire is unused by any zmq client:

    def cast(self, msg_id, topic, data):
        self.outq.send([str(topic), str(msg_id), str('cast'),
                        _serialize(data)])

    def consume(self, sock):
        data = sock.recv()
        ...
        topic, msg_id, style, in_msg = data

It might be nice to clean this up, but backwards compat issues are clearly a concern

Perhaps it would be sensible to re-purpose this as a message format version

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/21790
Committed: http://github.com/openstack/oslo-incubator/commit/f1e5d569b6c9ceb6d7a4b338db9186e4f9c2fb7b
Submitter: Jenkins
Branch: master

commit f1e5d569b6c9ceb6d7a4b338db9186e4f9c2fb7b
Author: Eric Windisch <email address hidden>
Date: Tue Feb 12 11:46:24 2013 -0500

    Support RPC envelopes in impl_zmq

    This patch began as a set
    of tests verifying the functionality of
    sending and receiving RPC envelopes when
    using impl_zmq. It was discovered that
    when enabled, RPC envelopes were not
    actually working,

    The ZeroMQ driver includes its own envelopes.
    This patch introduce versioning to that
    envelope, eliminating the previously reserved
    'style' field.

    A new iteration of the zeromq-envelope is
    introduced, 'impl_zmq_v2'. It specifies
    that the zeromq-envelope should be followed
    by an unpacked array representing key value
    pairs of the standard RPC Envelope.

    Because the key-values of the RPC Envelope
    can be successfully transformed with bytes(),
    this prevents the need to double-serialize
    the content traversing the message bus.

    Also removes some unused imports.

    Closes bug 1123709
    Closes bug 1055446

    Change-Id: Ib04e3d092c9596146f1048d3502ac248496d313b