glpi: Refs #2243: really delete machines

Really delete machines from GLPI without put them in trash.

We use to achieve this webservices glpi plugin:

https://forge.indepnet.net/projects/webservices/wiki/Wiki

You have to install it and set a user/password for accessing the
deleteObjects method:

https://forge.indepnet.net/projects/webservices/wiki/GlpideleteObjects

Python side, we use python-glpi lib:

https://github.com/mcphargus/python-glpi