Add os-volume_upload_image action to volumeactions (#240)

* Add os-volume_upload_image action to volumeactions

* Code updates to align with style guide
diff --git a/openstack/blockstorage/extensions/volumeactions/results.go b/openstack/blockstorage/extensions/volumeactions/results.go
index b5695b7..634b04d 100644
--- a/openstack/blockstorage/extensions/volumeactions/results.go
+++ b/openstack/blockstorage/extensions/volumeactions/results.go
@@ -17,6 +17,11 @@
 	gophercloud.ErrResult
 }
 
+// UploadImageResult contains the response body and error from a UploadImage request.
+type UploadImageResult struct {
+	gophercloud.ErrResult
+}
+
 // ReserveResult contains the response body and error from a Get request.
 type ReserveResult struct {
 	gophercloud.ErrResult