Expand tutorial to include exit scanning

Doing an operation for all exits with a certain characteristic is a reasonably common task, for instance to check relay speeds or look for malicious exits.

'Check for ssl strip on all Russian exits' would be a natural extension of our client usage tutorial, and would exhibit quite a bit of controller functionality none of the other tutorials do at present.

This would involve three steps...

1. Write a script that we will use for the tutorial example.
2. Include it among our tutorial unit tests.
3. Expand our tutorial to walk visitors through how it works.