raft: use the channel instead of sleep to make test case reliable
raft: use the channel instead of sleep to make test case reliable

coreos/etcd,xiang90/etcd,rchicoli/etcd,whuwxl/etcd,fanminshi/etcd,handsomesun/etcd,lumjjb/etcd,li-ang/etcd,tguangch/etcd,insequent/etcd,armstrongli/etcd,YuleiXiao/etcd,mqliang/etcd,hongchaodeng/etcd,lorneli/etcd,ajityagaty/etcd,rchicoli/etcd,heyitsanthony/etcd,plasticbox/etcd,ajityagaty/etcd,etcd-io/etcd,endocode/etcd,glevand/coreos--etcd,heyitsanthony/etcd,endocode/etcd,li-ang/etcd,lorneli/etcd,mkumatag/etcd,jlamillan/etcd,whuwxl/etcd,mqliang/etcd,qqsun8819/etcd,bluebreezecf/etcd,ravigadde/etcd,coreos/etcd,etcd-io/etcd,handsomesun/etcd,YuleiXiao/etcd,insequent/etcd,rnaveiras/etcd,ajityagaty/etcd,tguangch/etcd,rnaveiras/etcd,joshix/etcd,mqliang/etcd,bdarnell/etcd,CrazyJvm/etcd,cockroachdb/etcd,ravigadde/etcd,yudai/etcd,vimalk78/etcd,bluebreezecf/etcd,mkumatag/etcd,mickep76/etcd,cockroachdb/etcd,sinsharat/etcd,sebrandon1/etcd,plasticbox/etcd,gyuho/etcd,mkumatag/etcd,a-robinson/etcd,glevand/coreos--etcd,sinsharat/etcd,qqsun8819/etcd,lumjjb/etcd,hongchaodeng/etcd,yudai/etcd,a-robinson/etcd,armstrongli/etcd,mickep76/etcd,dannysauer/etcd,visheshnp/etcd,gyuho/etcd,CrazyJvm/etcd,xiang90/etcd,vimalk78/etcd,jlamillan/etcd,bdarnell/etcd,visheshnp/etcd,akauppi/etcd,sebrandon1/etcd,rnaveiras/etcd,etcd-io/etcd,joshix/etcd,akauppi/etcd,fanminshi/etcd,dannysauer/etcd