Since different projects can have different configurations for what
the maximum value of the "Code-Review" label is in Gerrit, this teaches
presubmit_support to inspect the maximum configured value and see who
has granted it (the same behavior as the Submit button in Gerrit itself).

R=andybons@chromium.org, martiniss@chromium.org, tandrii@chromium.org
BUG=630738

Review-Url: https://codereview.chromium.org/2178673002