Combine the fields that will be used for content transformation
(content-type, codec, and group version) into a single struct in client,
and then pass that struct into the rest client and request. Set the
content-type when sending requests to the server, and accept the content
type as primary.
Will form the foundation for content-negotiation via the client.
If not, using `go test -count=n` would make them pile up and ultimately
get to the limit of open files:
client_test.go:522: expected an error, got Get http://127.0.0.1:46070/api: dial tcp 127.0.0.1:46070: socket: too many open files
Steps to reproduce (no longer fails):
godep go test -short -run '^$' -o test .
./test -test.run '^TestGetSwaggerSchema' -test.count 100
Note that this might not fail if your `ulimit -n` is not low enough.
