fix bug: two same volumeId in different collections

1, there will be two leader when master server startup in a few seconds
2, raft server will get a leader even there is only one master, so there is no need to do hard code to set the server to be leader

weed/topology/topology.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"math/rand"
 	"sync"
+	"time"
 
 	"github.com/chrislusf/raft"
 
@@ -65,26 +66,26 @@ func (t *Topology) IsLeader() bool {
 		if t.RaftServer.State() == raft.Leader {
 			return true
 		}
-		if t.RaftServer.Leader() == "" {
-			return true
-		}
 	}
 	return false
 }
 
 func (t *Topology) Leader() (string, error) {
 	l := ""
+	count := 3
+	for count > 0 {
 		if t.RaftServer != nil {
 			l = t.RaftServer.Leader()
 		} else {
 			return "", errors.New("Raft Server not ready yet!")
 		}
-
-	if l == "" {
-		// We are a single node cluster, we are the leader
-		return t.RaftServer.Name(), nil
+		if l != "" {
+			break
+		} else {
+			time.Sleep(time.Duration(5-count) * time.Second)
+		}
+		count -= 1
 	}
-
 	return l, nil
 }