msi: {virt,remote}-viewer depends on libxml2
    
    Currently libxml2 is pulled as an indirect dependency when virt-viewer
    is built with support to ovirt or libvirt (pulled by rest or libvirt,
    respectively). However, {virt,remote}-viewer itself depends on libxml2
    and not having it as an explicit dependency will cause errors on opening
    remote-viewer when it is built without support to ovirt/libvirt.