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

4479:07:16

running SlapOS.Eggs.UnitTest-Master.Python2

4479:07:04

running SlapOS.Eggs.UnitTest-Master.Python3

4479:06:50

running Wendelin.UnitTest-Master

4479:07:13