Test the system before auto updating the production environment

[marco-buttu]

In #4 we added yum autoupdate. This should be a temporary solution, because we do not want the production environment to be updated automatically right before or during observations, without any previous check. We should operate in this way:

• during the nightly build, check for updates in the development environment, and in case update the dev machines and run the DISCOS automatic tests
• in case the tests pass, update the production environment