Treat any output directory test command as error.

Surfaces any communications from the remote end during file
uploads. For example, we might get notifications if we're logging in
with the wrong user. Rather than swallow these, let's show them to the
user.

communicator/ssh/communicator.go

@@ -413,7 +413,12 @@ func (c *comm) sftpUploadFile(path string, input io.Reader, client *sftp.Client,
 
 	// find out if destination is a directory (this is to replicate rsync behavior)
 	testDirectoryCommand := fmt.Sprintf(`test -d "%s"`, path)
-	cmd := &packer.RemoteCmd{Command: testDirectoryCommand}
+	var stdout, stderr bytes.Buffer
+	cmd := &packer.RemoteCmd{
+		Command: testDirectoryCommand,
+		Stdout:  &stdout,
+		Stderr:  &stderr,
+	}
 
 	err := c.Start(cmd)
 
@@ -422,6 +427,12 @@ func (c *comm) sftpUploadFile(path string, input io.Reader, client *sftp.Client,
 		return err
 	}
 	cmd.Wait()
+	if stdout.Len() > 0 {
+		return fmt.Errorf("%s", stdout.Bytes())
+	}
+	if stderr.Len() > 0 {
+		return fmt.Errorf("%s", stderr.Bytes())
+	}
 	if cmd.ExitStatus == 0 {
 		if fi == nil {
 			return fmt.Errorf("Upload path is a directory, unable to continue.")
@@ -579,7 +590,12 @@ func (c *comm) scpUploadSession(path string, input io.Reader, fi *os.FileInfo) e
 
 	// find out if destination is a directory (this is to replicate rsync behavior)
 	testDirectoryCommand := fmt.Sprintf(`test -d "%s"`, path)
-	cmd := &packer.RemoteCmd{Command: testDirectoryCommand}
+	var stdout, stderr bytes.Buffer
+	cmd := &packer.RemoteCmd{
+		Command: testDirectoryCommand,
+		Stdout:  &stdout,
+		Stderr:  &stderr,
+	}
 
 	err := c.Start(cmd)
 
@@ -588,6 +604,12 @@ func (c *comm) scpUploadSession(path string, input io.Reader, fi *os.FileInfo) e
 		return err
 	}
 	cmd.Wait()
+	if stdout.Len() > 0 {
+		return fmt.Errorf("%s", stdout.Bytes())
+	}
+	if stderr.Len() > 0 {
+		return fmt.Errorf("%s", stderr.Bytes())
+	}
 	if cmd.ExitStatus == 0 {
 		if fi == nil {
 			return fmt.Errorf("Upload path is a directory, unable to continue.")