Improve/Fix Runtime Submit Consumer Selection

[GlenDC]

The runtime is used to process HTTP Requests for HTTP Clients. Consumers are provided by the client operation. Right now the selection process is as simple, as selecting the first one available in the array of given consumers.

This could use some improvement.

Relevant TODO: https://github.com/go-openapi/runtime/blob/master/client/runtime.go#L231

[GlenDC]

Relevant TODO: https://github.com/go-openapi/runtime/blob/master/client/request.go#L157