Missing --offline support for new tracks

[ebadyano]

Our standard tracks like geonames, geopoint and so one have files.txt with the data to be downloaded for --offline usage. And that dowload.sh script is using to download them without rally-setup

Many new tracks are missing this file and also a few more complex benchmarks may need dowload.sh script to be updated to support non flat data directoris structure (eg elastic/security, elastic/logs tracks)