Add ZeroMQ RPC backend

Now prevents more than one RPC backend selection.
(ZeroMQ, Qpid, and Rabbit are mutually exclusive)

Configure quantum and cinder to use ZeroMQ

Adds qpid to cinder config.

Change-Id: I229c4c632213a303d097d4a029e986598073665a
diff --git a/lib/cinder b/lib/cinder
index 1bad5c0..5f0b255 100644
--- a/lib/cinder
+++ b/lib/cinder
@@ -115,6 +115,8 @@
 
     if is_service_enabled qpid ; then
         iniset $CINDER_CONF DEFAULT rpc_backend cinder.openstack.common.rpc.impl_qpid
+    elif is_service_enabled zeromq; then
+        iniset $CINDER_CONF DEFAULT rpc_backend nova.openstack.common.rpc.impl_zmq
     elif [ -n "$RABBIT_HOST" ] &&  [ -n "$RABBIT_PASSWORD" ]; then
         iniset $CINDER_CONF DEFAULT rabbit_host $RABBIT_HOST
         iniset $CINDER_CONF DEFAULT rabbit_password $RABBIT_PASSWORD