Bug#39848 events_bugs fails sporadically on pushbuild
            (missing rows in table event_log)
     Details: Reimplement the subtest for BUG 28924
              - check if the number of rows within the table
                event_log changes but don't print rows
                because the number varies depending on
                load on testing box
              - shift DROP USER befor DROP EVENT
                = Subtest fits again to old bug
              - remove no more needed comments + variables
  Bug#39863 events_bugs fails sporadically on pushbuild 
            (extra processes in I_S.PROCESSLIST)
     Details: Abort with appropriate message to the protocol if
              release_lock() does not has the intended effect.
              This cannot prevent problems caused by the probably
              buggy release_lock() but it reveals if we had a
              problem in this area.
  Bug#39978 main.events_bugs does not clean up
     Detail: Restore global.event_scheduler = ON at end of test
  Bug#39569 events_bugs fails sporadically on pushbuild
            (should have failed with errno 1539)
     Detail: Set $wait_timeout to 4 instead of 2
- Fix two instabilities (result sets pulled from processlist in
  subtest for bug 16407) which were found during tests with high
  parallel I/O load
- Minor improvements of formatting
  Details:
  - Add comments
  - Remove tabs and trailing blanks
  - Add line breaks for better readability