Improve socket selection when there are no incoming sockets

[Matt-Esch]

If the provided host list is large and there are not incoming connections, tchannel exhaustively connects to all of the nodes in the host list regardless of the necessity to do this.

I think this behavior needs to be improved for services that are consuming from tchannel services and not advertising themselves. This effectively means an improvement in the peer selection code. lb_pool avoids connecting to the entire host list by favoring open connections and supplying a max sockets option.

[Matt-Esch]

cc: @Raynos

[Raynos]

This is a good idea.

At the same time; everyone should advertise().