Fix SSL tunnel socket

Maybe I'm not using the SSLTunnelConnection correctly but this looks like an internal problem - without this change, I'm getting the following error:
```
pyVmomi.VmomiSupport.HostConnectFault: (vim.fault.HostConnectFault) {
   dynamicType = <unset>,
   dynamicProperty = (vmodl.DynamicProperty) [],
   msg = 'must be _socket.socket, not socket',
   faultCause = <unset>,
   faultMessage = (vmodl.LocalizableMessage) []
}
```