fix leadership transfer code readability

.changelog/11242.txt

@@ -1,3 +1,3 @@
 ```release-note:bug
-leader: When a leader leave the cluster try to transfer leadership before leaving.
+raft: Consul leaders will attempt to transfer leadership to another server as part of gracefully leaving the cluster.
 ```

agent/consul/server.go

@@ -941,6 +941,22 @@ func (s *Server) Shutdown() error {
 	return nil
 }
 
+func (s *Server) attemptLeadershipTransfer() (success bool) {
+	leadershipTransferVersion := version.Must(version.NewVersion(LeaderTransferMinVersion))
+
+	ok, _ := ServersInDCMeetMinimumVersion(s, s.config.Datacenter, leadershipTransferVersion)
+	if !ok {
+		return false
+	}
+
+	future := s.raft.LeadershipTransfer()
+	if err := future.Error(); err != nil {
+		s.logger.Error("failed to transfer leadership, removing the server", "error", err)
+		return false
+	}
+	return true
+}
+
 // Leave is used to prepare for a graceful shutdown of the server
 func (s *Server) Leave() error {
 	s.logger.Info("server starting leave")
@@ -966,25 +982,9 @@ func (s *Server) Leave() error {
 		}
 
 		if minRaftProtocol >= 2 && s.config.RaftConfig.ProtocolVersion >= 3 {
-			// Check if we can do a leadership transfer instead of removing our selves
-			leadershipTransferVersion := version.Must(version.NewVersion(LeaderTransferMinVersion))
-			removeServer := false
-			if ok, _ := ServersInDCMeetMinimumVersion(s, s.config.Datacenter, leadershipTransferVersion); !ok {
-				// Transfer leadership to another node then leave the cluster
-				future := s.raft.LeadershipTransfer()
-				if err := future.Error(); err != nil {
-					s.logger.Error("failed to transfer leadership, removing the server", "error", err)
-					// leadership transfer failed, fallback to removing the server from raft
-					removeServer = true
-				} else {
-					// we are not leader anymore, continue the flow to leave as follower
-					isLeader = false
-				}
+			if s.attemptLeadershipTransfer() {
+				isLeader = false
 			} else {
-				// Leadership transfer is not available in the current version, fallback to removing the server from raft
-				removeServer = true
-			}
-			if removeServer {
 				future := s.raft.RemoveServer(raft.ServerID(s.config.NodeID), 0, 0)
 				if err := future.Error(); err != nil {
 					s.logger.Error("failed to remove ourself as raft peer", "error", err)