Fix net.box test

test/box/net.box.result

@@ -1758,9 +1758,9 @@ nb = net.new('localhost:3392', {
 });
 ---
 ...
-nb.error;
+nb.error:find('timed out') ~= nil;
 ---
-- Operation timed out
+- true
 ...
 nb:close();
 ---

test/box/net.box.test.lua

@@ -701,7 +701,7 @@ nb = net.new('localhost:3392', {
     wait_connected = true, console = true,
     connect_timeout = 0.01
 });
-nb.error;
+nb.error:find('timed out') ~= nil;
 nb:close();
 -- we must get peer closed
 nb = net.new('localhost:3392', {