update_engine: Place enterprise rollback save marker file

- There are now two types of rollback. One that does a full powerwash
  and one that save some system state.
- When an enterprise rollback powerwash is scheduled, place a marker
  file to tell the shutdown process to save data before rebooting.
- This lets rollback preserve additional data over a powerwash that
  can be restored later.
- Change a few places that were using is_rollback to save_rollback_data
  to be explicit.

BUG=chromium:955463
TEST=unittests

Change-Id: I9f18319e711e425a6e712dd319e03bcc6ddd0a1b
Reviewed-on: https://chromium-review.googlesource.com/1414030
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/mock_update_attempter.h b/mock_update_attempter.h
index d97163d..c39fb62 100644
--- a/mock_update_attempter.h
+++ b/mock_update_attempter.h
@@ -30,12 +30,13 @@
  public:
   using UpdateAttempter::UpdateAttempter;
 
-  MOCK_METHOD8(Update,
+  MOCK_METHOD9(Update,
                void(const std::string& app_version,
                     const std::string& omaha_url,
                     const std::string& target_channel,
                     const std::string& target_version_prefix,
                     bool rollback_allowed,
+                    bool rollback_data_save_requested,
                     int rollback_allowed_milestones,
                     bool obey_proxies,
                     bool interactive));