Fix watchers

Working with graphite-data.rb and adding some checks, I noticed that we were not restarting sensu-client and sensu-server when needed.

This PR covers the cases I found:

- Update to plugin/graphite-data.rb was not picked up by the sensu-client until restart (due to embedded ruby maybe?)
- Addition of swap-out graphite check did not get distributed to the clients until sensu-server was restarted.

Also noticed that the `set roles` fix I made earlier wasn't working. I've fixed it properly now for the 'minion has no roles' case.