avoid panic debugging ssh key

builder/googlecompute/builder.go

@@ -66,6 +66,7 @@ func (b *Builder) Run(ctx context.Context, ui packer.Ui, hook packer.Hook) (pack
 		multistep.If(b.config.PackerDebug && b.config.Comm.SSHPrivateKeyFile == "",
 			&communicator.StepDumpSSHKey{
 				Path: fmt.Sprintf("gce_%s.pem", b.config.PackerBuildName),
+				SSH:  &b.config.Comm.SSH,
 			},
 		),
 		&StepImportOSLoginSSHKey{

helper/communicator/step_debug_ssh_keys.go

@@ -13,18 +13,15 @@ import (
 // keypair somewhere.
 type StepDumpSSHKey struct {
 	Path string
+	SSH  *SSH
 }
 
 func (s *StepDumpSSHKey) Run(_ context.Context, state multistep.StateBag) multistep.StepAction {
 	ui := state.Get("ui").(packer.Ui)
 
-	// Put communicator config into state so we can pass it to provisioners
-	// for specialized interpolation later
-	comm := state.Get("communicator_config").(Config)
-
 	ui.Message(fmt.Sprintf("Saving key for debug purposes: %s", s.Path))
 
-	err := ioutil.WriteFile(s.Path, comm.SSHPrivateKey, 0700)
+	err := ioutil.WriteFile(s.Path, s.SSH.SSHPrivateKey, 0700)
 	if err != nil {
 		state.Put("error", fmt.Errorf("Error saving debug key: %s", err))
 		return multistep.ActionHalt