Add `reuse_address(true)` to client connections

[EliSnow]

I'm experimenting with using hyper to run load tests and ephemeral port exhaustion is a real problem. Can reuse_address(true) be added to the client connection code (here, and here, I believe)?

Would making the change here also apply to tls connections made using hyper_tls?

[seanmonstar]

I haven't thought this through at all, so some questions: would this cause problems for people who weren't expecting this? Could people assume that they normally would have different ports? If so, perhaps this would just be an option on HttpConnector?

[EliSnow]

I would be perfectly fine with just having the option of enabling it. Does that mean hyper_tls would have to add an option for reuse_address to apply to https connections?

[seanmonstar]

hyper-tls has a constructor that allows you configure a connector first, so it wouldn't need any changes.