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/update_attempter.h b/update_attempter.h
index 6c25eb2..82b81ce 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -85,6 +85,7 @@
                       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);
@@ -341,6 +342,7 @@
                              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);