benchmark: enable grpc error logging on stderr
benchmark: enable grpc error logging on stderr

Lets you see connection errors (e.g., if tls is misconfigured)

rchicoli/etcd,CrazyJvm/etcd,bdarnell/etcd,ravigadde/etcd,mkumatag/etcd,CrazyJvm/etcd,sebrandon1/etcd,rnaveiras/etcd,armstrongli/etcd,dannysauer/etcd,insequent/etcd,whuwxl/etcd,lumjjb/etcd,joshix/etcd,ravigadde/etcd,vimalk78/etcd,cockroachdb/etcd,cockroachdb/etcd,bluebreezecf/etcd,visheshnp/etcd,lumjjb/etcd,rnaveiras/etcd,plasticbox/etcd,glevand/coreos--etcd,gyuho/etcd,handsomesun/etcd,li-ang/etcd,xiang90/etcd,ajityagaty/etcd,etcd-io/etcd,joshix/etcd,yudai/etcd,sebrandon1/etcd,whuwxl/etcd,mkumatag/etcd,heyitsanthony/etcd,lorneli/etcd,jlamillan/etcd,heyitsanthony/etcd,mkumatag/etcd,sinsharat/etcd,gyuho/etcd,ajityagaty/etcd,sinsharat/etcd,visheshnp/etcd,handsomesun/etcd,rchicoli/etcd,insequent/etcd,mickep76/etcd,etcd-io/etcd,YuleiXiao/etcd,dannysauer/etcd,ajityagaty/etcd,mqliang/etcd,a-robinson/etcd,li-ang/etcd,lorneli/etcd,rnaveiras/etcd,fanminshi/etcd,a-robinson/etcd,mickep76/etcd,YuleiXiao/etcd,mqliang/etcd,tguangch/etcd,mqliang/etcd,glevand/coreos--etcd,jlamillan/etcd,plasticbox/etcd,akauppi/etcd,bluebreezecf/etcd,akauppi/etcd,bdarnell/etcd,coreos/etcd,armstrongli/etcd,xiang90/etcd,fanminshi/etcd,etcd-io/etcd,yudai/etcd,tguangch/etcd,vimalk78/etcd,coreos/etcd