Ports are sometimes not freed up when CTRL-C or otherwise abnormal termination occurs

[usergenic]

I don't know if the karma ports are being held open too, but the proxy ports are apparently left unavailable. Maybe do some more due-diligence, catch SIGTERM and close server explicitly in those cases etc.

[usergenic]

FWIW this is going to be less an issue with Travis CI, for example, and more an issue with local development.