[RTADPA BW tests] Small cleanups after !359

FYI @lugrazet

Goes with LHCbPR2HD!271

This MR just cleans up the logging in the bandwidth tests a little bit after !359 (merged), and grabs the latest HLT2 output from the current_hlt2_output directory on /eos/. I think it's neat to have all the transient files we need to live in one directory.

I also checked while here that the download of files for the BW test does not happen if the file is already present, as we thought. The log should now give us more info on whether the download happens or not, so we can spot this more easily in the future.