Update Rakefile

* Upgraded PE from 3.0.1 to 3.1.0
* Upgraded CentOS from 6.3 to 6.4
Making the iso_url for CentOS more generic.
Removing deprecated use of 'fqdn'.

Should be '@fqdn'.
Merge pull request #155 from klynton/bugfix/puppeterror

Removing deprecated use of 'fqdn'.
A somewhat icky way of only managing the key once.

The `puppet_enterprise::license` manages the license file on the
master, but only after it exists. So we do the opposite. We manage
the file, but only when it doesn't exist.

On first run, we'll manage it, but on subsequent runs PE will take over.
Fix the Debian iso_url and actually fix the CentOS iso_url.
Merge pull request #157 from binford2k/ticket/TRAINVM-42/fix_license_file_management

A somewhat icky way of only managing the key once.
Adding note to the Initial Setup list to check for missing gems.
Merge pull request #158 from fnaard/add_gem_to_initial_setup

Adding note to the Initial Setup list to check for missing gems.
Fix the hiera shortcut

- without writing the defaults.yaml file, agent runs
  on student machines won't be able to see the existence
  of teams (if only master.puppetlabs.vm.yaml exists)
Merge pull request #159 from casharma/fix/cap/hiera

Fix the hiera shortcut

@casharma +1!
Fix advanced - manage the pe cert, bump version
Merge pull request #160 from casharma/advanced/bumpversion

Fix advanced - manage the pe cert, bump version
Setting the background in vim to dark by default.
Merge pull request #161 from klynton/improvement/vim-bg-fix

Setting the background in vim to dark by default.
Merge pull request #154 from klynton/bugfix-centosupgrade

Update PE and CentOS iso_url in Rakefile.
Added virtualbox, xorriso to initial setup, specified 32-bit CentOS ISOs
Punctuation cleanup
Merge pull request #162 from gsarjeant/readme_add_setup_steps

Add steps to the "Initial Setup" section of the README

Thanks @gsarjeant.
Adding a note about using homebrew.