Targeting integration with CernVM 3

The following improvements have been made:

* only the VAF client has been kept: [elastiq](https://github.com/dberzano/elastiq) has been detached
* more intuitive main configuration file name (`vaf.conf` instead of `common.before`)
* automatic configuration creation if not found
* creation of a RPM package through [fpm](https://github.com/jordansissel/fpm)

The RPM package will be installed by default with CernVM 3, but it is not CernVM specific.