pkg/pbutil: use leveled log

pkg/pbutil/pbutil.go

@@ -14,7 +14,11 @@
 
 package pbutil
 
-import "log"
+import "github.com/coreos/pkg/capnslog"
+
+var (
+	plog = capnslog.NewPackageLogger("github.com/coreos/etcd/pkg", "flags")
+)
 
 type Marshaler interface {
 	Marshal() (data []byte, err error)
@@ -27,14 +31,14 @@ type Unmarshaler interface {
 func MustMarshal(m Marshaler) []byte {
 	d, err := m.Marshal()
 	if err != nil {
-		log.Panicf("marshal protobuf type should never fail: %v", err)
+		plog.Panicf("marshal should never fail (%v)", err)
 	}
 	return d
 }
 
 func MustUnmarshal(um Unmarshaler, data []byte) {
 	if err := um.Unmarshal(data); err != nil {
-		log.Panicf("unmarshal protobuf type should never fail: %v", err)
+		plog.Panicf("unmarshal should never fail (%v)", err)
 	}
 }