Match facter version in puppet-agen6
puppet-agent 6 runs with facter version < 4 so run puppet6 CI tests with facter < 4.
Also undo the unhelpeful update absolute_classname-check from 3 back to 2 to mimic what we had in previous incarnation 1.6.2
puppet-agent 6 runs with facter version < 4 so run puppet6 CI tests with facter < 4.
Also undo the unhelpeful update absolute_classname-check from 3 back to 2 to mimic what we had in previous incarnation 1.6.2