break telegraf registry into separate package

this is for supporting external plugins.

external plugins will depend on a few telegraf interface types, as well
as a common telegraf registry.

this will allow external and internal plugins to both share this package
and make it easier to vendor/version the whole thing semantically, which
will make it easier to keep plugins supported across build and telegraf
versions.

see #1717

plugins/outputs/amon/amon.go

@@ -10,7 +10,7 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type Amon struct {

plugins/outputs/amqp/amqp.go

@@ -9,8 +9,8 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 
 	"github.com/streadway/amqp"
 )

plugins/outputs/cloudwatch/cloudwatch.go

@@ -12,7 +12,7 @@ import (
 
 	"github.com/influxdata/telegraf"
 	internalaws "github.com/influxdata/telegraf/internal/config/aws"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type CloudWatch struct {

plugins/outputs/datadog/datadog.go

@@ -11,7 +11,7 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type Datadog struct {

plugins/outputs/discard/discard.go

@@ -2,7 +2,7 @@ package discard
 
 import (
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type Discard struct{}

plugins/outputs/file/file.go

@@ -6,8 +6,8 @@ import (
 	"os"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type File struct {

plugins/outputs/graphite/graphite.go

@@ -9,8 +9,8 @@ import (
 	"time"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type Graphite struct {

plugins/outputs/graylog/graylog.go

@@ -8,7 +8,7 @@ import (
 	ejson "encoding/json"
 	"fmt"
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 	"io"
 	"math"
 	"net"

plugins/outputs/influxdb/influxdb.go

@@ -10,7 +10,7 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
 	"github.com/influxdata/telegraf/metric"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 
 	"github.com/influxdata/telegraf/plugins/outputs/influxdb/client"
 )

plugins/outputs/instrumental/instrumental.go

@@ -12,9 +12,9 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
 	"github.com/influxdata/telegraf/metric"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
 	"github.com/influxdata/telegraf/plugins/serializers/graphite"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 var (

plugins/outputs/kafka/kafka.go

@@ -6,8 +6,8 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 
 	"github.com/Shopify/sarama"
 )

plugins/outputs/kinesis/kinesis.go

@@ -10,8 +10,8 @@ import (
 
 	"github.com/influxdata/telegraf"
 	internalaws "github.com/influxdata/telegraf/internal/config/aws"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type KinesisOutput struct {

plugins/outputs/librato/librato.go

@@ -11,8 +11,8 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers/graphite"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 // Librato structure for configuration and client

plugins/outputs/mqtt/mqtt.go

@@ -7,8 +7,8 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 
 	paho "github.com/eclipse/paho.mqtt.golang"
 )

plugins/outputs/nats/nats.go

@@ -7,8 +7,8 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type NATS struct {

plugins/outputs/nsq/nsq.go

@@ -6,8 +6,8 @@ import (
 	"github.com/nsqio/go-nsq"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type NSQ struct {

plugins/outputs/opentsdb/opentsdb.go

@@ -10,7 +10,7 @@ import (
 	"strings"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type OpenTSDB struct {

plugins/outputs/prometheus_client/prometheus_client.go

@@ -10,7 +10,7 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 	"github.com/prometheus/client_golang/prometheus"
 )
 

plugins/outputs/registry.go

@@ -1,13 +0,0 @@
-package outputs
-
-import (
-	"github.com/influxdata/telegraf"
-)
-
-type Creator func() telegraf.Output
-
-var Outputs = map[string]Creator{}
-
-func Add(name string, creator Creator) {
-	Outputs[name] = creator
-}

plugins/outputs/riemann/riemann.go

@@ -10,7 +10,7 @@ import (
 
 	"github.com/amir/raidman"
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type Riemann struct {

plugins/outputs/riemann_legacy/riemann.go

@@ -9,7 +9,7 @@ import (
 
 	"github.com/amir/raidman"
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 const deprecationMsg = "E! Error: this Riemann output plugin will be deprecated in a future release, see https://github.com/influxdata/telegraf/issues/1878 for more details & discussion."

plugins/outputs/socket_writer/socket_writer.go

@@ -6,8 +6,8 @@ import (
 	"strings"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/registry/outputs"
 )
 
 type SocketWriter struct {