AMQP: Use a named topic exchange; prep for Activity Monitor.

Instead of using default (direct) exchange, declare a topic exchange "boulder" for all queues. This permits a pub/sub model.

amqp-rpc.go

@@ -24,7 +24,9 @@ import (
 // XXX: I *think* these constants are appropriate.
 // We will probably want to tweak these in the future.
 const (
-	AmqpExchange     = ""
+	AmqpExchange     = "boulder"
+	AmqpExchangeType = "topic"
+	AmqpInternal     = false
 	AmqpDurable      = false
 	AmqpDeleteUnused = false
 	AmqpExclusive    = false
@@ -48,6 +50,18 @@ func amqpConnect(url string) (ch *amqp.Channel, err error) {
 
 // A simplified way to declare and subscribe to an AMQP queue
 func amqpSubscribe(ch *amqp.Channel, name string) (msgs <-chan amqp.Delivery, err error) {
+	err = ch.ExchangeDeclare(
+		AmqpExchange,
+		AmqpExchangeType,
+		AmqpDurable,
+		AmqpDeleteUnused,
+		AmqpInternal,
+		AmqpNoWait,
+		nil)
+	if err != nil {
+		log.Fatalf("Could not declare exchange: %s", err)
+	}
+
 	q, err := ch.QueueDeclare(
 		name,
 		AmqpDurable,