Removing cronjob by default

- Adding a cronjob to sync with master.puppetlabs.vm is bad since
  the learning VM will be affected, and for advanced, the master of
  masters is called classroom.puppetlabs.vm
- What this means is that by default, the agents won't try to sync with
  the master
Fix the @pe_tarball mess
Merge pull request #235 from casharma/fix/ubuntu-installer

Fix/ubuntu installer