Something wrong when run "bin/SyncProducer" in two or more threads(specified by -T)

**BUG REPORT**
The running result will be like（both master an release 2.2）:
```
./SyncProducer -n XX -g XX -t XX -i XX -T 2
nameserver: XX
topic: XX
groupname: XX
produce content: msgbody for test
msg count: 1
thread count: 2
send failed: Type: MQClientException , msg: No route info of this topic: XX,error:-1,in file line:434
send failed: Type: MQClientException , msg: No route info of this topic: XX,error:-1,in file line:434
send failed: Type: MQClientException , msg: No route info of this topic: XX,error:-1,in file line:434
send failed: Type: MQClientException , msg: No route info of this topic: XX,error:-1,in file line:434
send failed: Type: MQClientException , msg: No route info of this topic: XX,error:-1,in file line:434
send failed: Type: MQClientException , msg: No route info of this topic: XX,error:-1,in file line:434
per msg time: 56ms
========================finished==============================
tps: 3

```