Add a cherry-pick exception.

If someone is trying to cherry-pick back to aosp, don't force them
to use --no-verify, allow it.

Right now, the only form of cherry-pick allowed is:

  cherry picked from

Test: Ran on a commit with the message and without and observed that
Test: with the cherry pick message, no error, without, error message.
Change-Id: I27581f782cdc1a1c4fa207a3aae392c0d434eb5a