This update provides the meat for the image download feature
within the Core.   Minimal testing was done with the CLI as the
adapters have not implemented this feature so far.

Change-Id: I771340876d9aa1f368642cd44a433ced3df52673
diff --git a/adapters/simulated_olt/adaptercore/simulated_olt.go b/adapters/simulated_olt/adaptercore/simulated_olt.go
index bb6883a..aa6e248 100644
--- a/adapters/simulated_olt/adaptercore/simulated_olt.go
+++ b/adapters/simulated_olt/adaptercore/simulated_olt.go
@@ -222,22 +222,22 @@
 	return errors.New("UnImplemented")
 }
 
-func (so *SimulatedOLT) Download_image(device *voltha.Device, request *voltha.ImageDownload) error {
-	return errors.New("UnImplemented")
+func (so *SimulatedOLT) Download_image(device *voltha.Device, request *voltha.ImageDownload)  (*voltha.ImageDownload, error) {
+	return nil, errors.New("UnImplemented")
 }
 
-func (so *SimulatedOLT) Get_image_download_status(device *voltha.Device, request *voltha.ImageDownload) error {
-	return errors.New("UnImplemented")
+func (so *SimulatedOLT) Get_image_download_status(device *voltha.Device, request *voltha.ImageDownload)  (*voltha.ImageDownload, error) {
+	return nil, errors.New("UnImplemented")
 }
 
-func (so *SimulatedOLT) Cancel_image_download(device *voltha.Device, request *voltha.ImageDownload) error {
-	return errors.New("UnImplemented")
+func (so *SimulatedOLT) Cancel_image_download(device *voltha.Device, request *voltha.ImageDownload)  (*voltha.ImageDownload, error) {
+	return nil, errors.New("UnImplemented")
 }
 
-func (so *SimulatedOLT) Activate_image_update(device *voltha.Device, request *voltha.ImageDownload) error {
-	return errors.New("UnImplemented")
+func (so *SimulatedOLT) Activate_image_update(device *voltha.Device, request *voltha.ImageDownload)  (*voltha.ImageDownload, error) {
+	return nil, errors.New("UnImplemented")
 }
 
-func (so *SimulatedOLT) Revert_image_update(device *voltha.Device, request *voltha.ImageDownload) error {
-	return errors.New("UnImplemented")
+func (so *SimulatedOLT) Revert_image_update(device *voltha.Device, request *voltha.ImageDownload)  (*voltha.ImageDownload, error) {
+	return nil, errors.New("UnImplemented")
 }