Uses an unconditional `chcon`

[cgwalters]

There are a few instances of an unconditional chcon -t in this code, which will fail on systems with SELinux disabled like Ubuntu (in the GHA runners). One can use e.g. selinuxenabled to check for this.

Hardcoding file types is also wrong in general (selinux policies can be customized). I'd try using chcon --reference instead.

(But really, it's not entirely clear to me why this project goes to the effort it does to put images outside of the default libvirt storage pools?)