openstack builder: Set image_type to "image"

so that built images are treated as images and not as snapshots.

Fixes: GH-3038

builder/openstack/image_config.go

@@ -18,6 +18,17 @@ func (c *ImageConfig) Prepare(ctx *interpolate.Context) []error {
 		errs = append(errs, fmt.Errorf("An image_name must be specified"))
 	}
 
+	// By default, OpenStack seems to create the image with an image_type of
+	// "snapshot", since it came from snapshotting a VM. A "snapshot" looks
+	// slightly different in the OpenStack UI and OpenStack won't show "snapshot"
+	// images as a choice in the list of images to boot from for a new instance.
+	// See https://github.com/mitchellh/packer/issues/3038
+	if c.ImageMetadata == nil {
+		c.ImageMetadata = map[string]string{"image_type": "image"}
+	} else if c.ImageMetadata["image_type"] == "" {
+		c.ImageMetadata["image_type"] = "image"
+	}
+
 	if len(errs) > 0 {
 		return errs
 	}