tools: add update handler

Add an UpdateHandler to handle each step of the update process.

This code was already in place but is now handled via an UpdateHandler
object.

Tested: Not yet tested.
Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I36cd1b94d8e2c0788d09805d935738d86e6e33de
diff --git a/tools/main.cpp b/tools/main.cpp
index 5868d11..536cde1 100644
--- a/tools/main.cpp
+++ b/tools/main.cpp
@@ -175,8 +175,8 @@
         /* The parameters are all filled out. */
         try
         {
-            host_tool::updaterMain(&blob, handler.get(), imagePath,
-                                   signaturePath);
+            host_tool::UpdateHandler updater(&blob, handler.get());
+            host_tool::updaterMain(&updater, imagePath, signaturePath);
         }
         catch (const host_tool::ToolException& e)
         {