raft: handle non voting members correctly in stepdown procedure

For leader stepdown purposes a non voting member is not different
from a node outside of the config. The patch makes relevant code paths
to check for both conditions.

raft/fsm.cc

@@ -536,9 +536,11 @@ void fsm::tick_leader() {
 
     if (state.stepdown) {
         logger.trace("tick[{}]: stepdown is active", _my_id);
-        if (leader_state().tracker.find(_my_id) == nullptr) {
+        auto me = leader_state().tracker.find(_my_id);
+        if (me == nullptr || !me->can_vote) {
             // Do not abort stepdown if not part of the current
-            // config.
+            // config or non voting member since the node cannot
+            // be a leader any longer
         } else if (*state.stepdown <= _clock.now()) {
             logger.trace("tick[{}]: cancel stepdown", _my_id);
             // Cancel stepdown (only if the leader is part of the cluster)
@@ -995,7 +997,8 @@ void fsm::send_timeout_now(server_id id) {
     logger.trace("send_timeout_now[{}] send timeout_now to {}", _my_id, id);
     send_to(id, timeout_now{_current_term});
     leader_state().timeout_now_sent = id;
-    if (leader_state().tracker.find(_my_id) == nullptr) {
+    auto me = leader_state().tracker.find(_my_id);
+    if (me == nullptr || !me->can_vote) {
         logger.trace("send_timeout_now[{}] become follower", _my_id);
         become_follower({});
     }