[JENKINS-49112] Revert use of Files.newBufferedReader() in Util.loadFile() (#3259)
[JENKINS-49112] Revert use of Files.newBufferedReader() in Util.loadFile() (#3259)

* [JENKINS-49112] Revert use of Files.newBufferedReader() in Util.loadFile()

This partially reverts 67076834a24f03b832ab03b1bf9b96e05a5da81e.

* Restore the use of StringBuilder and reading into buf

DanielWeber/jenkins,MarkEWaite/jenkins,MarkEWaite/jenkins,bkmeneguello/jenkins,dariver/jenkins,damianszczepanik/jenkins,daniel-beck/jenkins,recena/jenkins,recena/jenkins,MarkEWaite/jenkins,jenkinsci/jenkins,stephenc/jenkins,ErikVerheul/jenkins,jenkinsci/jenkins,patbos/jenkins,MarkEWaite/jenkins,godfath3r/jenkins,patbos/jenkins,ikedam/jenkins,andresrc/jenkins,recena/jenkins,godfath3r/jenkins,kohsuke/hudson,bkmeneguello/jenkins,pjanouse/jenkins,godfath3r/jenkins,Vlatombe/jenkins,sathiya-mit/jenkins,rsandell/jenkins,Vlatombe/jenkins,sathiya-mit/jenkins,v1v/jenkins,MarkEWaite/jenkins,DanielWeber/jenkins,kohsuke/hudson,jenkinsci/jenkins,v1v/jenkins,damianszczepanik/jenkins,daniel-beck/jenkins,oleg-nenashev/jenkins,andresrc/jenkins,aldaris/jenkins,bkmeneguello/jenkins,patbos/jenkins,viqueen/jenkins,bkmeneguello/jenkins,Vlatombe/jenkins,batmat/jenkins,ikedam/jenkins,v1v/jenkins,oleg-nenashev/jenkins,aldaris/jenkins,amuniz/jenkins,kohsuke/hudson,rsandell/jenkins,kohsuke/hudson,stephenc/jenkins,andresrc/jenkins,damianszczepanik/jenkins,andresrc/jenkins,stephenc/jenkins,godfath3r/jenkins,stephenc/jenkins,pjanouse/jenkins,recena/jenkins,amuniz/jenkins,sathiya-mit/jenkins,godfath3r/jenkins,ErikVerheul/jenkins,aldaris/jenkins,viqueen/jenkins,viqueen/jenkins,sathiya-mit/jenkins,bkmeneguello/jenkins,aldaris/jenkins,daniel-beck/jenkins,damianszczepanik/jenkins,sathiya-mit/jenkins,Jochen-A-Fuerbacher/jenkins,andresrc/jenkins,pjanouse/jenkins,rsandell/jenkins,Jochen-A-Fuerbacher/jenkins,patbos/jenkins,ikedam/jenkins,patbos/jenkins,stephenc/jenkins,MarkEWaite/jenkins,amuniz/jenkins,daniel-beck/jenkins,Jochen-A-Fuerbacher/jenkins,dariver/jenkins,aldaris/jenkins,dariver/jenkins,stephenc/jenkins,aldaris/jenkins,viqueen/jenkins,v1v/jenkins,sathiya-mit/jenkins,godfath3r/jenkins,MarkEWaite/jenkins,Vlatombe/jenkins,dariver/jenkins,jenkinsci/jenkins,kohsuke/hudson,recena/jenkins,oleg-nenashev/jenkins,ErikVerheul/jenkins,oleg-nenashev/jenkins,damianszczepanik/jenkins,damianszczepanik/jenkins,daniel-beck/jenkins,patbos/jenkins,stephenc/jenkins,rsandell/jenkins,dariver/jenkins,DanielWeber/jenkins,amuniz/jenkins,oleg-nenashev/jenkins,pjanouse/jenkins,batmat/jenkins,patbos/jenkins,kohsuke/hudson,MarkEWaite/jenkins,viqueen/jenkins,ikedam/jenkins,Vlatombe/jenkins,amuniz/jenkins,aldaris/jenkins,amuniz/jenkins,DanielWeber/jenkins,daniel-beck/jenkins,ErikVerheul/jenkins,jenkinsci/jenkins,rsandell/jenkins,ikedam/jenkins,Jochen-A-Fuerbacher/jenkins,batmat/jenkins,damianszczepanik/jenkins,DanielWeber/jenkins,kohsuke/hudson,andresrc/jenkins,ErikVerheul/jenkins,damianszczepanik/jenkins,rsandell/jenkins,godfath3r/jenkins,Jochen-A-Fuerbacher/jenkins,kohsuke/hudson,ErikVerheul/jenkins,daniel-beck/jenkins,DanielWeber/jenkins,ikedam/jenkins,batmat/jenkins,jenkinsci/jenkins,dariver/jenkins,bkmeneguello/jenkins,jenkinsci/jenkins,ikedam/jenkins,Vlatombe/jenkins,v1v/jenkins,batmat/jenkins,rsandell/jenkins,amuniz/jenkins,daniel-beck/jenkins,ikedam/jenkins,dariver/jenkins,DanielWeber/jenkins,batmat/jenkins,pjanouse/jenkins,batmat/jenkins,oleg-nenashev/jenkins,Jochen-A-Fuerbacher/jenkins,v1v/jenkins,pjanouse/jenkins,ErikVerheul/jenkins,Vlatombe/jenkins,andresrc/jenkins,pjanouse/jenkins,viqueen/jenkins,recena/jenkins,jenkinsci/jenkins,rsandell/jenkins,bkmeneguello/jenkins,oleg-nenashev/jenkins,sathiya-mit/jenkins,viqueen/jenkins,v1v/jenkins,Jochen-A-Fuerbacher/jenkins,recena/jenkins