ui_test_core: trigger a change event after setFile

This is what browsers do when user selects a file.
4 jobs for fix/event-setFile (queued for 4 seconds)
Status Job ID Name Coverage
  External
running ERP5.CodingStyleTest-Master

9406:42:37

running SlapOS.Eggs.UnitTest-Master.Python2

9406:42:24

running SlapOS.Eggs.UnitTest-Master.Python3

9406:42:11

running Wendelin.UnitTest-Master

9406:42:33