teach travis to run integration tests with live node

[dckc]

Run our own node? Use testnet?

[JoshOrndorff]

travis could wget the right package, apt install it, some version of rnode run or freshr or something. But we'd maybe have to hack some kind of wait 30 seconds for the node to start or something.

I think letting testnet problems block your git workflow isn't a good idea yet.