Add cleanup trap to integration test script (#4075)
Add cleanup trap to integration test script (#4075)

The integration test script spins up Python webservers. This trap will
ensure that those webservers are shutdown at exit.
letsencrypt/letsencrypt,jsha/letsencrypt,jsha/letsencrypt,stweil/letsencrypt,lmcro/letsencrypt,stweil/letsencrypt,lmcro/letsencrypt,letsencrypt/letsencrypt