treat EOF and ErrClosedPipe in websocket connections as uninteresting

both occur in various states of disconnectedness

app/controls.go

 package app
 
 import (
-	"io"
 	"net/http"
 	"net/rpc"
 
@@ -84,7 +83,7 @@ func handleProbeWS(cr ControlRouter) CtxHandlerFunc {
 			return
 		}
 		defer cr.Deregister(ctx, probeID, id)
-		if err := codec.WaitForReadError(); err != nil && err != io.EOF && !xfer.IsExpectedWSCloseError(err) {
+		if err := codec.WaitForReadError(); err != nil && !xfer.IsExpectedWSCloseError(err) {
 			log.Errorf("Error on websocket: %v", err)
 		}
 	}

common/xfer/websocket.go

@@ -167,8 +167,7 @@ func (p *pingingWebsocket) Close() error {
 // IsExpectedWSCloseError returns boolean indicating whether the error is a
 // clean disconnection.
 func IsExpectedWSCloseError(err error) bool {
-	return websocket.IsCloseError(
-		err,
+	return err == io.EOF || err == io.ErrClosedPipe || websocket.IsCloseError(err,
 		websocket.CloseNormalClosure,
 		websocket.CloseGoingAway,
 		websocket.CloseNoStatusReceived,