Send params on the URL for DELETEs

This is the root of all* the weird issues with etcd today - DELETE was trying to send params in the body of the request, and since etcd wasn't expecting to have to read a body they were being munged into the method of the following request which the Gorilla MUX, used by etcd internally, helpfully hid by returning a 404 rather than logging the fact that garbage was coming in.

I suspect this whole conditional would be more robust if it was flipped (I'm sorry). As in, I think POST and PUT are exceptional in having a body, and that most other request types won't have bodies.