Xenstat exporter

[Richard Kojedzinszky]

Dear developers,

I have implemented a simple xenstat exporter, which exports xen statistics accessible via C interface.

Please have a look at it: https://github.com/euronetzrt/xenstat-exporter

Also, please review, comments are welcome.

And if you find it suitable, it could be listed under Prometheus main page as an exporter.

We find the exported metrics very useful, although grafana dashboards have not been published.

Regards,

Richard