Allow specifying <firmware>GUID</firmware> to check any version exists
Allow specifying <firmware>GUID</firmware> to check any version exists

If the version is not specified then treat it as just 'exists'.

hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd