Change duration -> internal and implement private gopsutil methods

outputs/amon/amon.go

@@ -9,14 +9,14 @@ import (
 	"strings"
 
 	"github.com/influxdb/influxdb/client/v2"
-	"github.com/influxdb/telegraf/duration"
+	"github.com/influxdb/telegraf/internal"
 	"github.com/influxdb/telegraf/outputs"
 )
 
 type Amon struct {
 	ServerKey    string
 	AmonInstance string
-	Timeout      duration.Duration
+	Timeout      internal.Duration
 
 	client *http.Client
 }

outputs/datadog/datadog.go

@@ -11,13 +11,13 @@ import (
 	"strings"
 
 	"github.com/influxdb/influxdb/client/v2"
-	"github.com/influxdb/telegraf/duration"
+	"github.com/influxdb/telegraf/internal"
 	"github.com/influxdb/telegraf/outputs"
 )
 
 type Datadog struct {
 	Apikey  string
-	Timeout duration.Duration
+	Timeout internal.Duration
 
 	apiUrl string
 	client *http.Client

outputs/influxdb/influxdb.go

@@ -9,7 +9,7 @@ import (
 	"strings"
 
 	"github.com/influxdb/influxdb/client/v2"
-	"github.com/influxdb/telegraf/duration"
+	"github.com/influxdb/telegraf/internal"
 	"github.com/influxdb/telegraf/outputs"
 )
 
@@ -22,7 +22,7 @@ type InfluxDB struct {
 	Database  string
 	UserAgent string
 	Precision string
-	Timeout   duration.Duration
+	Timeout   internal.Duration
 
 	conns []client.Client
 }

outputs/librato/librato.go

@@ -8,7 +8,7 @@ import (
 	"net/http"
 
 	"github.com/influxdb/influxdb/client/v2"
-	"github.com/influxdb/telegraf/duration"
+	"github.com/influxdb/telegraf/internal"
 	"github.com/influxdb/telegraf/outputs"
 )
 
@@ -16,7 +16,7 @@ type Librato struct {
 	ApiUser   string
 	ApiToken  string
 	SourceTag string
-	Timeout   duration.Duration
+	Timeout   internal.Duration
 
 	apiUrl string
 	client *http.Client

outputs/mqtt/mqtt.go

@@ -11,7 +11,7 @@ import (
 
 	paho "git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.golang.git"
 	"github.com/influxdb/influxdb/client/v2"
-	"github.com/influxdb/telegraf/duration"
+	"github.com/influxdb/telegraf/internal"
 	"github.com/influxdb/telegraf/outputs"
 )
 
@@ -24,7 +24,7 @@ type MQTT struct {
 	Username    string
 	Password    string
 	Database    string
-	Timeout     duration.Duration
+	Timeout     internal.Duration
 	TopicPrefix string
 
 	Client *paho.Client