Add passive mode exchange declaration option to amqp consumer input (#3995)

plugins/inputs/amqp_consumer/README.md

@@ -19,6 +19,8 @@ The following defaults are known to work with RabbitMQ:
   url = "amqp://localhost:5672/influxdb"
   ## AMQP exchange
   exchange = "telegraf"
+  ## Exchange passive mode
+  exchange_passive = false
   ## AMQP queue name
   queue = "telegraf"
   ## Binding Key

plugins/inputs/amqp_consumer/amqp_consumer.go

@@ -20,6 +20,8 @@ type AMQPConsumer struct {
 	URL string
 	// AMQP exchange
 	Exchange string
+	// Exchange passive mode
+	ExchangePassive bool
 	// Queue Name
 	Queue string
 	// Binding Key
@@ -58,6 +60,8 @@ func (a *AMQPConsumer) SampleConfig() string {
   url = "amqp://localhost:5672/influxdb"
   ## AMQP exchange
   exchange = "telegraf"
+  ## Exchange passive mode
+  exchange_passive = false
   ## AMQP queue name
   queue = "telegraf"
   ## Binding Key
@@ -174,15 +178,27 @@ func (a *AMQPConsumer) connect(amqpConf *amqp.Config) (<-chan amqp.Delivery, err
 		return nil, fmt.Errorf("Failed to open a channel: %s", err)
 	}
 
-	err = ch.ExchangeDeclare(
-		a.Exchange, // name
-		"topic",    // type
-		true,       // durable
-		false,      // auto-deleted
-		false,      // internal
-		false,      // no-wait
-		nil,        // arguments
-	)
+	if a.ExchangePassive == true {
+		err = ch.ExchangeDeclarePassive(
+			a.Exchange, // name
+			"topic",    // type
+			true,       // durable
+			false,      // auto-deleted
+			false,      // internal
+			false,      // no-wait
+			nil,        // arguments
+		)
+	} else {
+		err = ch.ExchangeDeclare(
+			a.Exchange, // name
+			"topic",    // type
+			true,       // durable
+			false,      // auto-deleted
+			false,      // internal
+			false,      // no-wait
+			nil,        // arguments
+		)
+	}
 	if err != nil {
 		return nil, fmt.Errorf("Failed to declare an exchange: %s", err)
 	}