message: hermes.rs: Propagate rather than panic on network errors
  Saw this during a sync:
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Io(Os { code: 16, kind: Other, message: "Device or resource busy" })', libcore/result.rs:945:5
diff: @@ -90,7 +90,7 @@ impl Api for HermesEndPoint {
  })
  });
  let now = SystemTime::now();
  - self.core.run(work).unwrap();
  + self.core.run(work)?;
  let time_elapsed = now.elapsed().unwrap();
  info!("Downloaded block in {}sec", time_elapsed.as_secs());
  }
  @@ -148,7 +148,7 @@ impl Api for HermesEndPoint {
  })
  });
  let now = SystemTime::now();
  - self.core.run(work).unwrap();
  + self.core.run(work)?;
  let time_elapsed = now.elapsed().unwrap();
  info!("Downloaded EPOCH in {}sec", time_elapsed.as_secs());
  }
  