Downloader only supports a single file to monitor

[briandoconnor]

The docs on gnos_download_file.pl indicate you pass in a file glob for checking by the download tool. But the code actually just does a "-e $file". So, at least, the docs need to be updated to make it clear it is a single file monitor.

[niall-byrne]

I have a possible solution to this implemented for the store and forward workflow, as a python script that can be called:

https://github.com/ICGC-TCGA-PanCancer/store-and-forward-workflow/blob/master/workflow/scripts/download_check.py