Kill WPT server with SIGINT instead of SIGTERM
Kill WPT server with SIGINT instead of SIGTERM

Prevents leaving behind several python processes after running tests

mzgol/jsdom,fiftin/jsdom,Zirro/jsdom,Joris-van-der-Wel/jsdom,mzgol/jsdom,snuggs/jsdom,fiftin/jsdom,Zirro/jsdom,tmpvar/jsdom,mzgol/jsdom,snuggs/jsdom,Joris-van-der-Wel/jsdom,Joris-van-der-Wel/jsdom,fiftin/jsdom,tmpvar/jsdom