Validate controller examples

@titanous 

dependent on #471 
I have rebased on master, updated the test to run `flynn-controller-examples` on the Flynn cluster, and added `script/generate-controller-examples` for generating locally to STDOUT (see [this diff](https://github.com/flynn/flynn/compare/07de075c06902900042d35709eca63e10022c914...19ebdc40afadca54243a0f6b5c0f8f77db300d06))