连接mysql出现如下错误：
Host 'host_name' is blocked because of many connection errors.
Unblock with 'mysqladmin flush-hosts'
it means that mysqld has received many connection requests from the given host that were interrupted in the middle
即：是mysql的服务端主动对某个指定ip/host的屏蔽。
可通过修改max_connect_errors修改上限
可通过执行mysqladmin flush-hosts命令刷新限制（使用另外一台没有被屏蔽的机器连接执行命令）
