TOP-1355: cnic writing speed issue monitoring

Add a workaround for all tests except one new in the performance_statistics folder Truncate long log message, we have it only in one place, so I did a pretty simple implementation, for Full logs DEBUG message can be inspected

flush_pps was increased to 8000 because we waited 40 minutes for 5 min scan, now it is 10. Ruby will calculate more accurate value in nearest future.