Fix YAMLDecoder Read behaviour

Make it adhere to the Read contract by returning the number of bytes
read.

staging/src/k8s.io/apimachinery/pkg/util/yaml/decoder.go

@@ -122,7 +122,7 @@ func (d *YAMLDecoder) Read(data []byte) (n int, err error) {
 	if left <= len(data) {
 		copy(data, d.remaining)
 		d.remaining = nil
-		return len(d.remaining), nil
+		return left, nil
 	}
 
 	// caller will need to reread

staging/src/k8s.io/apimachinery/pkg/util/yaml/decoder_test.go

@@ -22,12 +22,26 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"math/rand"
 	"reflect"
 	"strings"
 	"testing"
 )
 
+func TestYAMLDecoder(t *testing.T) {
+	d := `---
+stuff: 1
+	test-foo: 1
+`
+	s := NewDocumentDecoder(ioutil.NopCloser(bytes.NewReader([]byte(d))))
+	b := make([]byte, len(d))
+	n, err := s.Read(b)
+	if err != nil || n != len(d) {
+		t.Fatalf("unexpected body: %d / %v", n, err)
+	}
+}
+
 func TestSplitYAMLDocument(t *testing.T) {
 	testCases := []struct {
 		input  string