Allow for on-prem JAMF instances

[innowintay]

Thanks for this most recent update! I'm actually in the process of rolling out Backblaze using JAMF to my company and had just perfected my adaptations of the older script when I noticed this one had been updated to fix the error reporting.

I saw where you requested that we enter an issue before PRing any major changes. The way you had the JAMF URL scripted prevents anyone using JAMF on-prem from using this script without adaptation. I'm going to PR a change that not only allows users to enter the full FQDN but also ensures it strips the HTTP/HTTPS protocol if they should happen to include it.