[bug] Azure copyPartRange should stage block on destination

copyPartRange should stage a block on the destination.  This matters When
source and destination containers are different.

pkg/block/azure/multipart_block_writer.go

@@ -174,9 +174,9 @@ func getMultipartSize(ctx context.Context, container container.Client, objName s
 	return int64(size), nil
 }
 
-func copyPartRange(ctx context.Context, destinationContainer container.Client, destinationObjName string, sourceBlobURL blockblob.Client, startPosition, count int64) (*block.UploadPartResponse, error) {
+func copyPartRange(ctx context.Context, destinationContainer container.Client, destinationObjName string, sourceContainer blockblob.Client, startPosition, count int64) (*block.UploadPartResponse, error) {
 	base64BlockID := generateRandomBlockID()
-	_, err := sourceBlobURL.StageBlockFromURL(ctx, base64BlockID, sourceBlobURL.URL(),
+	_, err := destinationContainer.StageBlockFromURL(ctx, base64BlockID, sourceContainer.URL(),
 		&blockblob.StageBlockFromURLOptions{
 			Range: blob.HTTPRange{
 				Offset: startPosition,
@@ -188,7 +188,7 @@ func copyPartRange(ctx context.Context, destinationContainer container.Client, d
 	}
 
 	// add size and id to etag
-	response, err := sourceBlobURL.GetProperties(ctx, nil)
+	response, err := destinationContainer.GetProperties(ctx, nil)
 	if err != nil {
 		return nil, err
 	}