title: Chef/knife command to update clients after changing role
body: <p>After I boot up a server using Chef, if I've forgotten to include a recipe in a role (eg apache2::mod_ssl) is there a way to simply update the client without having to delete it and "knife server create" again?</p>
  
  <p>Even better, the servers are all registered with my Chef server (Opscode platform), so in theory they should be able to receive updates from Opscode after I push role changes to the platform.  Is this possible?  Or is it possible to have my server check the Chef server for changes on a regular interval, perhaps every 10 minutes?</p>