Add argument to disable yaml cronjob when factsource => yaml

The $::path variable was messing a lot with multiple distributions...

puppet agent -t  on centos : PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
puppet agent -t on debian: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
automated run (/etc/init.d/puppet) centos: PATH=/usr/bin:/sbin:/bin:/usr/sbin
automated run (/etc/init.d/puppet) debian: PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
(packages from puppetlabs: 3.6.2-1.el6 and 3.6.2-1puppetlabs1)