Rename ActionExitCode to ErrorCode

Nowadays ActionExitCode is used throughout the codebase so use a more
generic name to reflect this.

BUG=chromium:216507
TEST=unit tests pass

Change-Id: I23d1d7e2676443251dbc42ed137fd018aadfa8a3
Reviewed-on: https://gerrit.chromium.org/gerrit/49512
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
diff --git a/omaha_response_handler_action.cc b/omaha_response_handler_action.cc
index f494aa0..ad6a087 100644
--- a/omaha_response_handler_action.cc
+++ b/omaha_response_handler_action.cc
@@ -94,7 +94,7 @@
                    response.deadline.size());
   chmod(kDeadlineFile, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
 
-  completer.set_code(kActionCodeSuccess);
+  completer.set_code(kErrorCodeSuccess);
 }
 
 bool OmahaResponseHandlerAction::GetInstallDev(const std::string& boot_dev,