Use the product token for the user agent in more locations (#7378)

internal/internal_test.go

@@ -8,6 +8,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os/exec"
+	"regexp"
 	"testing"
 	"time"
 
@@ -480,3 +481,11 @@ func TestParseTimestamp(t *testing.T) {
 		})
 	}
 }
+
+func TestProductToken(t *testing.T) {
+	token := ProductToken()
+	// Telegraf version depends on the call to SetVersion, it cannot be set
+	// multiple times and is not thread-safe.
+	re := regexp.MustCompile(`^Telegraf/[^\s]+ Go/\d+.\d+.\d+$`)
+	require.True(t, re.MatchString(token), token)
+}