Revert "Revert "AU: do not copy filesystem during full updates""

This reverts commit d1cd325c3135d88498483da811b594ba6b91ce42

The problem that caused all autotests to fail with the original CL has now been rectified; lab devservers were updated to send the correct delta flag in their omaha response.

Change-Id: I664afb33f72856572baaa658cbd473c07271af36
Reviewed-on: https://gerrit.chromium.org/gerrit/56600
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/omaha_response_handler_action.cc b/omaha_response_handler_action.cc
index c85711b..c876d94 100644
--- a/omaha_response_handler_action.cc
+++ b/omaha_response_handler_action.cc
@@ -70,6 +70,7 @@
         kPrefsUpdateCheckResponseHash, response.hash))
         << "Unable to save the update check response hash.";
   }
+  install_plan_.is_full_update = !response.is_delta_payload;
 
   TEST_AND_RETURN(GetInstallDev(
       (!boot_device_.empty() ? boot_device_ : utils::BootDevice()),