using blocking cp method.

builder/amazon/chroot/communicator.go

 package chroot
 
 import (
+	"fmt"
 	"github.com/mitchellh/packer/packer"
 	"io"
 	"log"
@@ -21,7 +22,7 @@ type Communicator struct {
 func (c *Communicator) Start(cmd *packer.RemoteCmd) error {
 
 	chrootCommand := fmt.Sprintf("%s %s %s", c.ChrootCommand, c.Chroot, cmd.Command)
-	localcmd := exec.Command("/bin/sh", "-c", chrootCommand)
+	localCmd := exec.Command("/bin/sh", "-c", chrootCommand)
 	localCmd.Stdin = cmd.Stdin
 	localCmd.Stdout = cmd.Stdout
 	localCmd.Stderr = cmd.Stderr

builder/amazon/chroot/copy_files.go

 package chroot
 
 import (
-	"log"
+	"fmt"
 	"os/exec"
 )
 
-func copySingle(dst string, src string, copyCommand string) error {
+func copySingle(dest string, src string, copyCommand string) error {
 	cpCommand := fmt.Sprintf("sudo cp -fn %s %s", src, dest)
-	localcmd := exec.Command("/bin/sh", "-c", cpCommand)
-	log.Println(localcmd.Args)
-	out, err := localcmd.CombinedOutput()
-	if err != nil {
-		log.Println(err)
+	localCmd := exec.Command("/bin/sh", "-c", cpCommand)
+	if err := localCmd.Run(); err != nil {
+		return err
 	}
-	log.Printf("output: %s", out)
 	return nil
 }