message: metrics: actually return a 200 status code
  For whatever reason the page is returning a 404 status code at the
  moment. I haven't found exactly why, but this forces the status code on
  that page to be 200 when metrics are returned.
diff: use super::pool::Pool;
  use iron::headers::ContentType;
  use iron::prelude::*;
  +use iron::status::Status;
  use prometheus::{Encoder, IntGauge, TextEncoder};
  lazy_static! {
  @@ -35,6 +36,7 @@ pub fn metrics_handler(req: &mut Request) -> IronResult<Response> {
  ctry!(TextEncoder::new().encode(&families, &mut buffer));
  let mut resp = Response::with(buffer);
  + resp.status = Some(Status::Ok);
  resp.headers
  .set(ContentType("text/plain; version=0.0.4".parse().unwrap()));
  Ok(resp)
  