Failing docker builds will leave files owned as root

[Shados]

https://github.com/UnitedIncome/serverless-python-requirements/blob/c9d910cc40d95163f8894abfdefaf9c4fc33b505/lib/pip.js#L264-L269

^ This code never gets run if during the docker-run one of the Python package builds fails (e.g. due to missing some system dependency).

This will leave the download cache files owned by root, which will in turn prevent subsequent build attempts from working, due to this earlier attempt to open $downloadCacheDir/requriements.txt in write mode now being unable to succeed.

[pgrzesik]

Hey 👋 I'm closing this ticket as it looks like it's heavily outdated, we can of course reopen it if needed 👍