[RTA BW Tests] Remove dependence of rates from initial N_EVTS request

When the events in a file is less than N_EVTS (typically 1e5 currently), this isn't corrected for and all rates/retentions/BWs are a factor of N_FOUND / N_EVTS too small.

For now, fixed the N_EVTS to be process specific (thus allowing HLT1 to use 1e4 events to better match what is currently in it's file)

ToDo: Access the N_FOUND (grep the log file?) and propagate that through the rest of the work instead.