builder/openstack: validate ssh key name/file

This is a port for OpenStack of PR #4665

builder/openstack/run_config.go

@@ -56,6 +56,15 @@ func (c *RunConfig) Prepare(ctx *interpolate.Context) []error {
 
 	// Validation
 	errs := c.Comm.Prepare(ctx)
+
+	if c.SSHKeyPairName != "" {
+		if c.Comm.Type == "winrm" && c.Comm.WinRMPassword == "" && c.Comm.SSHPrivateKey == "" {
+			errs = append(errs, errors.New("A private_key_file must be provided to retrieve the winrm password when using ssh_keypair_name."))
+		} else if c.Comm.SSHPrivateKey == "" && !c.Comm.SSHAgentAuth {
+			errs = append(errs, errors.New("A private_key_file must be provided or ssh_agent_auth enabled when ssh_keypair_name is specified."))
+		}
+	}
+
 	if c.SourceImage == "" && c.SourceImageName == "" {
 		errs = append(errs, errors.New("Either a source_image or a source_image_name must be specified"))
 	} else if len(c.SourceImage) > 0 && len(c.SourceImageName) > 0 {