Sync rpc from oslo-incubator.

This patch includes fixes for:

 * kombu: Fix lack of reconnect when using mirrored queues
 * zmq: support rpc envelopes
 * zmq: Fix IPC direct topic routing.

Change-Id: I3e494d0c1b72ed19ab4f590c5d5496a9b202633c
Merge "Sync rpc from oslo-incubator."