Sync rpc from oslo-incubator.

This includes the following changes:

 * use oslo.config directly
 * implementation of rpc-amqp-fast-reply-queue
 * simplifications to bin/nova-rpc-zmq-receiver
 * add new join_consumer_pool API call
 * a bug fix to ensure kombu messages get acked even when an exception
   occurs in the message callback

Change-Id: I813ce0ee7d5442d7b5b0f9d477949adabc83174e
Merge "Sync rpc from oslo-incubator."