TravisCI: install and run the host tools

[ktemkin]

Ideally, we'd have the TravisCI script run the install for the host tools, and maybe check to ensure that we can run one of the scripts-- e.g. that greatfet info runs enough to not find a GreatFET.

This would help to prevent issues like #148 from being introduced. :)

[mnaberez]

Consider running a tool like pyflakes as part of the host tools CI to check code (not style). It will help find common mistakes like missing imports.

[ktemkin]

The current travis script does exercise installation of the host tools. Closing as done.