Override getSocketAddress() in TCPMemcachedNodeImpl to auto detect memcached instance ip change

When deploying memcached to k8s, it's probably that a memcached instance goes up & down. During the process, its hostname can be unchanged while its ip changes.

Therefore, we override the getSocketAddress() in TCPMemcachedNodeImpl to uncache ip for hostname to make it possible for Kylin to be able to auto detect memcached instance ip change.