Add Serializer plugins, and 'file' output plugin

plugins/outputs/mqtt/mqtt_test.go

@@ -3,7 +3,9 @@ package mqtt
 import (
 	"testing"
 
+	"github.com/influxdata/telegraf/plugins/serializers"
 	"github.com/influxdata/telegraf/testutil"
+
 	"github.com/stretchr/testify/require"
 )
 
@@ -13,8 +15,10 @@ func TestConnectAndWrite(t *testing.T) {
 	}
 
 	var url = testutil.GetLocalHost() + ":1883"
+	s, _ := serializers.NewInfluxSerializer()
 	m := &MQTT{
-		Servers: []string{url},
+		Servers:    []string{url},
+		serializer: s,
 	}
 
 	// Verify that we can connect to the MQTT broker