Prevent random failure using earliestTime()

If start date and stop date, just use DateTime() it can make the packing
list generated divergent by saving the form.

DateTime() includes hour, minutes and seconds, but ERP5 UI don't.

bt5/erp5_user_tutorial_ui_test/SkinTemplateItem/portal_skins/erp5_user_tutorial_ui_test/Zuite_setUpSalePackingListTest.xml

@@ -91,8 +91,8 @@ sale_order = portal.sale_order_module.newContent(\n
                                    source_administration=my_organisation.getRelativeUrl(),\n
                                    delivery_mode=\'delivery_mode/air\',\n
                                    order=\'order/normal\',\n
-                                   start_date=DateTime(),\n
-                                   stop_date=DateTime()+1,\n
+                                   start_date=DateTime().earliestTime(),\n
+                                   stop_date=DateTime().earliestTime()+1,\n
 )\n
 sale_order.setPriceCurrency(currency.getRelativeUrl())\n
 sale_order.setIncoterm(\'incoterm/cpt\')\n

bt5/erp5_user_tutorial_ui_test/bt/revision

-786
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+787
\ No newline at end of file