slapos_jio_ui_test: use data-date attribute to not have any locale conflict

See https://lab.nexedi.com/nexedi/erp5/blob/1b31fcbd12ede57079851aa198aa8d9e9f70e073/bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_datetimefield_js.js#L281

master/bt5/slapos_jio_ui_test/PathTemplateItem/portal_tests/slaposjs_zuite/testSlapOSJSInvoice.zpt

@@ -62,12 +62,12 @@
 
       <tr>
         <td>waitForElementPresent</td>
-        <td>//p[text()='10/20/2019']</td>
+        <td>//p[@data-date='2019-10-20']</td>
         <td></td>
       </tr>
       <tr>
         <td>click</td>
-        <td>//p[text()='10/20/2019']</td>
+        <td>//p[@data-date='2019-10-20']</td>
         <td></td>
       </tr>