container-toolbox: Use 'toolbx' as VARIANT_ID in os-release(5)

This is meant to distinguish OCI containers and images that are designed
specifically for Toolbx from others.  Toolbx containers are long-lasting
pet containers for interactive command line use, which makes them
substantially different from short-lived containers running services.

Therefore, it can be useful to be able to identify Toolbx containers and
images when generating statistics about Fedora usage.

https://pagure.io/Fedora-Council/tickets/issue/449
https://pagure.io/fedora-kickstarts/pull-request/1026

fedora-container-toolbox.ks

@@ -33,7 +33,7 @@ dnf-yum  # https://fedorahosted.org/fesco/ticket/1312#comment:29
 dnf-plugins-core
 -dosfstools
 -e2fsprogs
-fedora-release-container
+fedora-release-toolbx
 findutils
 flatpak-spawn
 fpaste