explicitly error out on bad pip install
explicitly error out on bad pip install

jvenezia/heroku-buildpack-python,pkumar-appd/python-buildpack,ad-m/heroku-buildpack-python,miraculixx/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,swanson/heroku-buildpack-python-ortools,AltSchool/heroku-buildpack-python,edenspiekermann-amsterdam/heroku-buildpack-python,gaumire/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,andrespires/python-buildpack,cloudfoundry/python-buildpack,wbrefvem/heroku-buildpack-python,skilljar/heroku-buildpack-python,Nazanin84/python-buildpack,jimlindeman/python-buildpack-collectd,pkumar-appd/python-buildpack,heroku/heroku-buildpack-python,cclauss/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,zakdoek/heroku-buildpack-django,gitricko/apt-python-buildpack,plangrid/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,benmurden/heroku-buildpack-python-ember,heroku/heroku-buildpack-python,andrespires/python-buildpack,zakdoek/heroku-buildpack-django,samuelhavron/heroku-buildpack-python,andela-brotich/wger-buildpack-python,Scalingo/python-buildpack,samuelhavron/heroku-buildpack-python,pkumar-appd/python-buildpack,edmorley/heroku-buildpack-python,slorg1/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,driftyco/heroku-buildpack-sphinx,jimlindeman/python-buildpack-collectd,cloudfoundry/python-buildpack,jimlindeman/python-buildpack-collectd,andrespires/python-buildpack,loanzen/heroku-buildpack-python,wbrefvem/heroku-buildpack-python,grivescorbett/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,ojacobson/heroku-buildpack-python,Nazanin84/python-buildpack,Scalingo/python-buildpack,gitricko/apt-python-buildpack,joshfriend/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,benmurden/heroku-buildpack-python-ember,smalleats/heroku-buildpack-python,doda/heroku-buildpack-python,gitricko/apt-python-buildpack,doda/heroku-buildpack-python,AltSchool/heroku-buildpack-python,cloudfoundry/python-buildpack,Nazanin84/python-buildpack,jamarparris/heroku-buildpack-python-swig,HanSooloo/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,ad-m/heroku-buildpack-python