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

10890:29:15

running SlapOS.Eggs.UnitTest-Master.Python2

10890:29:03

running SlapOS.Eggs.UnitTest-Master.Python3

10890:28:49

running Wendelin.UnitTest-Master

10890:29:12