API /IP support server ip

[liangyuanpeng]

API /IP return server ip, so it shoud be :

{
"origin":"xxx",
"server":"172.0.2.1"
}

[mccutchen]

I don't think we should add this, as it would likely reveal information about an instance's backend infrastructure (e.g. internal IP ranges) that should only be exposed after careful consideration.