Always use configured source credentials.
Always use configured source credentials.

Previously, it tried to make anonymous requests, then retried with
credentials if it got a 401 or 403.

This caused issues with many private gem servers.

Fixes #3297, #3296, #3180.

jaym/bundler,steved/bundler,PG-kura/bundler,chulkilee/bundler,mdorrance/bundler,Elffers/bundler,anil826/bundler,asutoshpalai/bundler,gregkare/bundler,byroot/bundler,ligi/bundler,danimashu/bundler,Wirachmat/bundler,ximus/bundler,EasonYi/bundler,mvz/bundler,roseweixel/bundler,neslom/bundler,simplybusiness/bundler,mpapis/bundler,patvice/bundler,simplybusiness/bundler,pjump/bundler,philnash/bundler,mvz/bundler,EasonYi/bundler,seanlinsley/bundler,steved/bundler,gregkare/bundler,pivotal-cf-experimental/bundler,ximus/bundler,chef/bundler,bundler/bundler,ngpestelos/bundler,frsyuki/bundler,lmtim/bundler,h4ck3rm1k3/bundler,byroot/bundler,elovelan/bundler,chulkilee/bundler,ngpestelos/bundler,jingweno/bundler,nju520/bundler,elovelan/bundler,zhangkuaiji/bundler,h4ck3rm1k3/bundler,Elffers/bundler,bundler/bundler,davydovanton/bundler,frsyuki/bundler,christer155/bundler,pivotal-cf-experimental/bundler,ipmobiletech/bundler,anil826/bundler,cdwort/bundler,mpapis/bundler,wenderjean/bundler,davydovanton/bundler,RochesterinNYC/bundler,chef/bundler,asymmetric/bundler,asymmetric/bundler,kohgpat/bundler,nju520/bundler,cdwort/bundler,jasonkarns/bundler,zhangkuaiji/bundler,bronzdoc/bundler,smlance/bundler,Wirachmat/bundler,sideci-sample/sideci-sample-bundler,pjump/bundler,kohgpat/bundler,masarakki/bundler,Eric-Guo/bundler,Teino1978-Corp/Teino1978-Corp-bundler,PG-kura/bundler,ligi/bundler,mattbrictson/bundler-1,smlance/bundler,lmtim/bundler,asutoshpalai/bundler,jingweno/bundler,tgxworld/bundler,agis-/bundler,wenderjean/bundler,agis-/bundler,jaym/bundler,cstrahan/bundler,danimashu/bundler,schaary/bundler,EthanK28/bundler,Teino1978-Corp/Teino1978-Corp-bundler,CorainChicago/bundler,sideci-sample/sideci-sample-bundler,joshsoftware/bundler,tgxworld/bundler,seanlinsley/bundler,jasonkarns/bundler,schaary/bundler,carpodaster/bundler,dilumnavanjana/bundler,carpodaster/bundler,mdorrance/bundler,AiyionPrime/bundler,cstrahan/bundler,Eric-Guo/bundler,EthanK28/bundler,joshsoftware/bundler,dilumnavanjana/bundler,philnash/bundler,neslom/bundler,RochesterinNYC/bundler,bronzdoc/bundler,suhastech/bundler,suhastech/bundler,robinboening/bundler,AiyionPrime/bundler,CorainChicago/bundler,patvice/bundler,christer155/bundler,TimMoore/bundler,masarakki/bundler,roseweixel/bundler,mattbrictson/bundler-1,robinboening/bundler,TimMoore/bundler,ipmobiletech/bundler