Update Appveyor build script to attempt to get log files upon build failure.
Update Appveyor build script to attempt to get log files upon build failure.

jinlmsft/Prajna,hongzhili/Prajna,hongzhili/Prajna,cloudRoutine/Prajna,jinlmsft/Prajna,MSRCCS/Prajna,dVakulen/Prajna,TonyAbell/Prajna,MSRCCS/Prajna,BrunoBozza/Prajna,MSRCCS/Prajna,BrunoBozza/Prajna,TonyAbell/Prajna,cloudRoutine/Prajna,jinlmsft/Prajna,dVakulen/Prajna,leizhangcn/Prajna,jinlmsft/Prajna,YuxiaoHu/Prajna,MSRCCS/Prajna,leizhangcn/Prajna,BrunoBozza/Prajna,YuxiaoHu/Prajna,BrunoBozza/Prajna