Add tests about centinel

[ben-jones]

@gsathya, do we have a framework to do this in? I think we could probably adjust network conditions with mininet, but this is somewhat tricky/annoying, especially in the context of a unit test and it doesn't address the problem of setting up tests for things that actually interfere with the network, like DNS injection.

I think we should do this, but if we actually want to setup a validation framework, it will be/could be a ton of work. (read ~week for each experiment if not more)

[rpanah]

@ben-jones I agree. While this can always be added later, I don't think it should be part of our Alpha release especially since the current set of experiments are simple and small enough to be tested by their respective authors.

[gsathya]

I don't think we should have this for Alpha release, but we should definitely do some sort of testing. Mininet and all seem out of scope for now -- I'd rather just mock the various network conditions and run the experiments. That should be easy enough to get started.