Never ship plugin.json.
Keep the plugin.json always as ghost and create the
%{_sharedstatedir}/vagrant/plugins.json file and
%{_datadir}/vagrant/plugins.json symlink in %post. Also, let the
scriplets always work with the symlink to the real file. This should
provide better compatibility with rpm-ostree.
The link could be dropped in F28-F29 timeframew:
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/SKJVY6KZYP24B4KOXLX3BBI5DWSJUEK5/