builder/googlecompute: only load secrets/private key if given

builder/googlecompute/config.go

@@ -163,6 +163,7 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	}
 	c.stateTimeout = stateTimeout
 
+	if c.ClientSecretsFile != "" {
 		// Load the client secrets file.
 		cs, err := loadClientSecrets(c.ClientSecretsFile)
 		if err != nil {
@@ -170,13 +171,16 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 				errs, fmt.Errorf("Failed parsing client secrets file: %s", err))
 		}
 		c.clientSecrets = cs
+	}
 
+	if c.PrivateKeyFile != "" {
 		// Load the private key.
 		c.privateKeyBytes, err = processPrivateKeyFile(c.PrivateKeyFile, c.Passphrase)
 		if err != nil {
 			errs = packer.MultiErrorAppend(
 				errs, fmt.Errorf("Failed loading private key file: %s", err))
 		}
+	}
 
 	// Check for any errors.
 	if errs != nil && len(errs.Errors) > 0 {