Ip white list for proxy

Current MaxScale's Authentication mechanism has a limit, MaxScale's host should be added to every

tuple, as descriped in the Configuration Docments;

If there is a ip white list mechanism, put MaxScale's host in the white list, Server Authentication skip those host in the list will let MaxScale be much easier to use, especially in cloud environment;

Proposal:
1. server privide a white ip list variable;
2. In mysql monitor, after connected to backend, set host to the white list;