builder/docker: create export dir if needed

builder/docker/step_export.go

@@ -3,6 +3,7 @@ package docker
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
@@ -26,6 +27,13 @@ func (s *StepExport) Run(state multistep.StateBag) multistep.StepAction {
 		return multistep.ActionHalt
 	}
 
+	// Make the directory we're exporting to if it doesn't exist
+	exportDir := filepath.Dir(config.ExportPath)
+	if err := os.MkdirAll(exportDir, 0755); err != nil {
+		state.Put("error", err)
+		return multistep.ActionHalt
+	}
+
 	// Open the file that we're going to write to
 	f, err := os.Create(config.ExportPath)
 	if err != nil {