When a template is marked as 'installed by package manager', but cannot be uninstalled there, trying to uninstall manually will result in the error "ERROR: VM installed by package manager: template-vm-name". Do as follows to be able to uninstall the template:
1. Check the state of `installed_by_rpm`
$ qvm-prefs template-vm-name
2. If `installed_by_rpm - True]`, mark the template as not installed by package manager