Binary downloads from GitHub sometimes fail, causing script to crash

[masonr]

As reported here: https://talk.lowendspirit.com/discussion/comment/45079/#Comment_45079

Preparing system for disk tests...chmod: cannot access './2020-11-13T15_19_27+08_00/disk/fio': No such file or directory

Curl command grabbing the fio binary from the github repo is failing silently, thus the chmod fails on the non-existent file.

Proposed solution:

1. add the "--retry #" flag to the curl command to allow multiple retries to download it (in case the first try fails)
2. add some better error handling to detect if it wasn't able to grab it for some reason and either skip the disk test (if doable) or simply alert and exit safely

[masonr]

Fixed in 203c9a0