Fixes #4798: Switch to CFEngine 3.6.0rc1 for Rudder

Co-Authored-By: Nicolas PERRON <nicolas.perron@normation.com>
Merge pull request #326 from Kegeruneku/ust_4798/int/4799_upgrade_to_cfengine_3_6

Fixes #4798: Switch to CFEngine 3.6.0rc1 for Rudder