etcdserver: log lease revoke error

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

etcdserver/server.go

@@ -770,7 +770,9 @@ func (s *EtcdServer) run() {
 					lid := lease.ID
 					s.goAttach(func() {
 						ctx := s.authStore.WithRoot(s.ctx)
-						s.LeaseRevoke(ctx, &pb.LeaseRevokeRequest{ID: int64(lid)})
+						if _, lerr := s.LeaseRevoke(ctx, &pb.LeaseRevokeRequest{ID: int64(lid)}); lerr != nil {
+							plog.Warningf("failed to revoke %016x (%q)", lid, lerr.Error())
+						}
 						leaseExpired.Inc()
 						<-c
 					})