officejs_ui_test: use a more relaxed selector for spreadsheet

When I run this test on chrome, the div has two classes, spreadsheet
and jexcel_tab, this fixes a failure that the element is not found in
erp5_officejs_ui_test:testFunctionalOfficeJSWebTable

bt5/erp5_officejs_ui_test/PathTemplateItem/portal_tests/officejs_ui_webtable_zuite/testJexcelEditor.zpt

@@ -78,7 +78,7 @@
 <!-- Wait for spreadsheet to be rendered by the gadget -->
 <tr>
   <td>waitForElementPresent</td>
-  <td>//div[@class='spreadsheet']</td>
+  <td>css=.spreadsheet</td>
   <td></td>
 </tr>
 <!-- Verify maximize button is present -->

bt5/erp5_officejs_ui_test/PathTemplateItem/portal_tests/officejs_ui_webtable_zuite/testOfficeJSWebTableEditor.zpt

@@ -116,7 +116,7 @@
 </tr>
 <tr>
   <td>waitForElementPresent</td>
-  <td>//div[@class='spreadsheet']</td>
+  <td>css=.spreadsheet</td>
   <td></td>
 </tr>
 <!-- Wait for editor completly loaded, this is workaround, wait for lock in renderjs -->