Provide default args: percpu=true and totalcpu=true for cpu plugin

Also if outputs.file is empty, write to stdout

closes #720

plugins/inputs/system/cpu.go

@@ -113,6 +113,10 @@ func totalCpuTime(t cpu.CPUTimesStat) float64 {
 
 func init() {
 	inputs.Add("cpu", func() telegraf.Input {
-		return &CPUStats{ps: &systemPS{}}
+		return &CPUStats{
+			PerCPU:   true,
+			TotalCPU: true,
+			ps:       &systemPS{},
+		}
 	})
 }

plugins/outputs/file/file.go

@@ -36,6 +36,11 @@ func (f *File) SetSerializer(serializer serializers.Serializer) {
 
 func (f *File) Connect() error {
 	writers := []io.Writer{}
+
+	if len(f.Files) == 0 {
+		f.Files = []string{"stdout"}
+	}
+
 	for _, file := range f.Files {
 		if file == "stdout" {
 			writers = append(writers, os.Stdout)