Improve algorithm for getting transport info.

[F483]

Currently all peers in the local routing table are sent stun requests. This is not very efficient as we must wait for all answers.

• Better would be to stun only one peer at a time until a result is found, but this requires some adaptation.
• There should also be a check to filter results only from public nodes, to ensure the the transport info is correct.
• Since the transport info is very unlikely to change, it should be cached once a correct result is found.

https://github.com/Storj/storjnode/blob/develop/storjnode/network/server.py#L247

[F483]

The impact of the current implementation is not noticeable so this is low priority for now.