parallel test runs per stack
parallel test runs per stack

benmurden/heroku-buildpack-python-ember,AltSchool/heroku-buildpack-python,heroku/heroku-buildpack-python,Scalingo/python-buildpack,benmurden/heroku-buildpack-python-ember,AltSchool/heroku-buildpack-python,ad-m/heroku-buildpack-python,ad-m/heroku-buildpack-python,skilljar/heroku-buildpack-python,Scalingo/python-buildpack,heroku/heroku-buildpack-python