Fix functions download error (streamnative#897)

* Fix functions download error

* Fix tests

Author: jiangpengcheng

pkg/ctl/functions/download.go

@@ -127,7 +127,7 @@ func doDownloadFunctions(vc *cmdutils.VerbCmd, funcData *utils.FunctionData) err
 	admin := cmdutils.NewPulsarClientWithAPIVersion(common.V3)
 
 	if funcData.Path != "" {
-		err := admin.Functions().DownloadFunction(funcData.DestinationFile, funcData.Path)
+		err := admin.Functions().DownloadFunction(funcData.Path, funcData.DestinationFile)
 		if err != nil {
 			return err
 		}

pkg/ctl/functions/upload_test.go

@@ -114,8 +114,8 @@ func TestUploadAndDownloadCommands(t *testing.T) {
 	downloadFilePath := "download-upload-file"
 	args = []string{
 		"download",
-		"--destination-file", pulsarPath,
-		"--path", downloadFilePath,
+		"--destination-file", downloadFilePath,
+		"--path", pulsarPath,
 	}
 	out, execErr, err = TestFunctionsCommands(downloadFunctionsCmd, args)
 	defer os.RemoveAll(downloadFilePath)