Refactor security and guest-agents config

- Move guest-agents from hypervisor modifier to independent optional feature
- Merge guest-agents/gui.ks into base.ks
- Remove security from required, add optional security modifier with off option
- Fix hypervisor-type modifier key normalization (underscore→hyphen)
- Add expand_variants() to handle list values in manifest
- Update all tests and expected recipes

fragments/desktop/vmm/packages.ks

@@ -1,8 +0,0 @@
-# VMM (Virtual Machine Manager) packages
-
-%packages --exclude-weakdeps
-
-virtual-manager
-libvirt-client-tools
-
-%end

fragments/desktop/vmm/post-scripts.ks

@@ -1,9 +0,0 @@
-# VMM post-installation scripts
-
-%post --erroronfail
-
-# Start libvirt service
-systemctl enable libvirtd
-systemctl start libvirtd
-
-%end