Improve errors logged while connecting

acid.go

@@ -692,6 +692,8 @@ func rpcKillOne(ctx context.Context, id int64) error {
 	if !ok {
 		return fmt.Errorf("%d: not a running task", id)
 	}
+	// XXX: This just fails whatever stage the task is in,
+	// not showing up meaningfully in the task state.
 	rt.cancel(errTaskInterrupted)
 	return nil
 }
@@ -1412,11 +1414,8 @@ func executorConnect(
 		// net.DNSError eats the cause, as in it cannot be unwrapped
 		// and tested for a particular subtype.
 		conn, err := d.DialContext(ctxDeadlined, "tcp", address)
-		if e := ctxDeadlined.Err(); e != nil {
+		if e := context.Cause(ctxDeadlined); e != nil {
 			// This may provide a little bit more information.
-			if err != nil {
-				return nil, err
-			}
 			return nil, e
 		}
 		if err != nil {