Check generated fstab for changes

[DieracDelta]

I had the unfortunate experience of accidentally swapping the mapping of servers, then deploying. E.g. I deployed my laptop configuration to my desktop on accident. This passed local deploy-rs checks, but resulted in my server mounting the filesystems wrong and crashing.

I don't know how difficult this would be to implement but it would be a cool feature to add a check for this to deploy-rs. This check would ensure that the filesystem currently mounted (current /etc/static/fstab) on the system(s) to deploy to isn't changed by the new configuration. If it is, one could prompt the user if they still want to deploy (because it might be an accident).

[balsoft]

Did auto-rollback/magic-rollback not help in that case? I don't think I like the idea of adding arbitrary checks with user interaction required, since often we do indeed want to deploy fstab changes, sometimes even from CI.