move conftest visibility tests and their setup into a class, accomodates @nicoddemus 's comment
move conftest visibility tests and their setup into a class, accomodates @nicoddemus 's comment

--HG--
branch : issue616

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