Use Gerrit style format for footers in Presubmit

This also fixes a bug where CQ keywords were added multiple times because it was
looking for them in the wrong place (new_description_lines instead of the footers).

Bug: skia:6667
Change-Id: I91232297343145884b3fe7c2e923373679cf029e
Reviewed-on: https://skia-review.googlesource.com/17704
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
1 file changed