More fixes for 'exec' mode

- Do not allow it when chef-zero is being used (chef client local mode)
  If you do, it only re-execs the worker process, which is not the
  process running the chef-zero server.
- Add argv on as well in case of a runlist override
- Skip the install notifier, cut out the middleman. If you include the
  ::install recipe, you want to install, and it will always happen after
  the remote_file. This fixes #65, at the cost of making a few more
  assumptions.