output the latest log of component when failed to start

question from user:
```
tiup 替换 tidb-server 可执行文件后，tiup cluster start出现 “Starting component tidb
	Starting instance tidb 172.16.5.69:4000
	tidb 172.16.5.69:4000 failed to start: timed out waiting for port 4000 to be started after 1m0s”
可是目标机器上 lsof -i:4000 确实没有被占用，那是怎么回事呢？
```

make the user know why failling to start more easily