etcdserver: stop raft after stopping apply scheduler

Was causing a pipeline leak.

etcdserver/server.go

@@ -537,9 +537,12 @@ func (s *EtcdServer) run() {
 	}
 
 	defer func() {
-		s.r.stop()
 		sched.Stop()
 
+		// must stop raft after scheduler-- etcdserver can leak rafthttp pipelines
+		// by adding a peer after raft stops the transport
+		s.r.stop()
+
 		s.wg.Wait()
 
 		// kv, lessor and backend can be nil if running without v3 enabled