raft: fix TestNodeProposeAddDuplicateNode
raft: fix TestNodeProposeAddDuplicateNode

Only send signal after applying conf change.
Or deadlock might happen if raft node receives
ready without conf change when the test server
is slow.

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