Revise DownloadManager API to handle concurrent calls

[cbalioglu]

When multiple processes in a distributed job attempt to download the same asset, we do not handle it in a race-free way if the file system is shared. Think of a way to avoid it in FileDownloadManager

[artemru]

@cbalioglu : actually I'm hitting this error when launching a lots of Sonar data pipeline in parallel on Stopes. Hopefully there's a retry mechanism, but otherwise it feel like P0 is a good priority for this issue !