Code review comment for lp:~le-chi-thu/lava-dispatcher/cache-tarballs-v1

Method names are updated. I use a directory to sync between lava-dispatcher instances for creation of tarballs cache. I think it is a safe and simple solution. The worse case is if the lava-dispatcher instance who is creating the tarballs, crashed, other instance will timeout (20 minutes) and continue to download the image and create the tarballs themselves.

The caching of download files can be replace by squid. This solution did not depend on that feature except reusing some help functions in the utils.py