test_result: display actual duration on test result

This is different from the total of durations of test result lines
because they are executed in parralel on different testnodes. The
actual duration is just the difference between start and stop, so
that we don't have to calculate.

bt5/erp5_test_result/SkinTemplateItem/portal_skins/erp5_test_result/TestResult_view.xml

@@ -96,6 +96,7 @@
                         <string>my_id</string>
                         <string>my_start_date</string>
                         <string>my_stop_date</string>
+                        <string>your_real_duration</string>
                       </list>
                     </value>
                 </item>