Don't return 1 when failing to add Gerrit CCs

This causes other automated tooling to think that the entire
upload has failed, when really only a small part of it has.

BUG=666160

Change-Id: I0d646e77c54330d642097aebe70ec145ae291267
Reviewed-on: https://chromium-review.googlesource.com/412281
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>

git_cl.py

@@ -2847,11 +2847,8 @@ class _GerritChangelistImpl(_ChangelistCodereviewBase):
     if change_desc.get_cced():
       cc.extend(change_desc.get_cced())
     if cc:
-      errors = gerrit_util.AddReviewers(
+      gerrit_util.AddReviewers(
           self._GetGerritHost(), self.GetIssue(), cc, is_reviewer=False)
-      if errors:
-        return 1
-
     return 0
 
   def _AddChangeIdToCommitMessage(self, options, args):