For actions, switch bool success into an exit code.

This way we can signal specific error conditions and then
send appropriate events to Omaha from the UpdateAttempter.

BUG=560
TEST=unit tests, gmerged and looked at logs

Review URL: http://codereview.chromium.org/3022008
diff --git a/update_attempter.h b/update_attempter.h
index 753b409..711c8ea 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -50,11 +50,11 @@
   void Update();
 
   // ActionProcessorDelegate methods:
-  void ProcessingDone(const ActionProcessor* processor, bool success);
+  void ProcessingDone(const ActionProcessor* processor, ActionExitCode code);
   void ProcessingStopped(const ActionProcessor* processor);
   void ActionCompleted(ActionProcessor* processor,
                        AbstractAction* action,
-                       bool success);
+                       ActionExitCode code);
 
   // Stop updating. An attempt will be made to record status to the disk
   // so that updates can be resumed later.