git-cl: use private instead of draft

The private mode is a better fit for how we want private
(e.g. security-critical) changes to be reviewed. Draft
was simply a placeholder until private was ready for use,
which it now is.

Bug: 721880, 722627
Change-Id: Ib7b76c555437f4ddc7ab2b0e7ce5a9f9ee8be825
Reviewed-on: https://chromium-review.googlesource.com/513243
Commit-Queue: Aaron Gable <agable@chromium.org>
Reviewed-by: Andrew Bonventre <andybons@chromium.org>

git_cl.py

@@ -2981,7 +2981,7 @@ class _GerritChangelistImpl(_ChangelistCodereviewBase):
     refspec_opts.append('notify=NONE')
 
     if options.private:
-      refspec_opts.append('draft')
+      refspec_opts.append('private')
 
     if options.topic:
       # Documentation on Gerrit topics is here: