make runtox.py not import external modules unless run as a script
make runtox.py not import external modules unless run as a script

Was not needed since the script actually does nothing unless run as a script.

--HG--
branch : jurko/tox_usage

doordash/pytest,wfxiang08/pytest,pytest-dev/pytest,abusalimov/pytest,tareqalayan/pytest,mdboom/pytest,Carreau/pytest,alfredodeza/pytest,inirudebwoy/pytest,MengJueM/pytest,Bachmann1234/pytest,ionelmc/pytest,mhils/pytest,davidszotten/pytest,hackebrot/pytest,chillbear/pytest,inirudebwoy/pytest,ojake/pytest,ericdill/pytest,JonathonSonesen/pytest,tomviner/pytest,bukzor/pytest,omarkohl/pytest,txomon/pytest,chiller/pytest,lukas-bednar/pytest,ionelmc/pytest,RonnyPfannschmidt/pytest,omarkohl/pytest,jb098/pytest,abusalimov/pytest,nicoddemus/repo-test,userzimmermann/pytest,chiller/pytest,JonathonSonesen/pytest,chillbear/pytest,mdboom/pytest,gabrielcnr/pytest,malinoff/pytest,untitaker/pytest,Bjwebb/pytest,pfctdayelise/pytest,ddboline/pytest,etataurov/pytest,The-Compiler/pytest,ropez/pytest,ericdill/pytest,Akasurde/pytest,vodik/pytest,MichaelAquilina/pytest,ojake/pytest,doordash/pytest,mhils/pytest,flub/pytest,vodik/pytest,pelme/pytest,ghostsquad/pytest,rouge8/pytest,nicoddemus/pytest,ropez/pytest,Bachmann1234/pytest,hpk42/pytest,bubenkoff/pytest,Bjwebb/pytest,skylarjhdownes/pytest,Haibo-Wang-ORG/pytest,userzimmermann/pytest,takluyver/pytest,gabrielcnr/pytest,hunse/pytest,oleg-alexandrov/pytest,vmalloc/dessert,The-Compiler/pytest,hpk42/pytest,jb098/pytest,Haibo-Wang-ORG/pytest,icemac/pytest,nicoddemus/pytest,jaraco/pytest,untitaker/pytest,oleg-alexandrov/pytest,bukzor/pytest,rmfitzpatrick/pytest,markshao/pytest,codewarrior0/pytest,pelme/pytest,wfxiang08/pytest,mbirtwell/pytest,rouge8/pytest,nicoddemus/repo-test,takluyver/pytest,mbirtwell/pytest,Carreau/pytest,bubenkoff/pytest,codewarrior0/pytest,hunse/pytest,lukas-bednar/pytest,eli-b/pytest,tgoodlet/pytest,icemac/pytest,MengJueM/pytest,ghostsquad/pytest,tomviner/pytest