Re-factor pgd_cookbook for Chef-CentOS

Remove Ubuntu functionality. Default cookbook is now a Centos-6.5 box.
yum-ius, yum-epel, yum-osuosl are now included cookbooks; yum and apt
cookbooks have been removed.

Cookbook depends on build-essential, yum, and yum-ius. No longer depends
on ubuntu and apt.

_centos.rb recipe has been added to setup centos machine. This file was
taken from the whats_fresh cookbook.

Remove Vagrantfile. Usernames are still 'Vagrant' because they don't need
to change at the moment.

bootsrap_user.rb has been removed because it served literally no purpose.

Minor key changes were made to database.rb recipe. settings.py which
didn't exist now symlinks to pgd/settings.py. This is an issue and will
be addressed later.

A few other miscellaneous centos-compatibility and naming fixes were put
in.
Address feedback for PR

Refs #6

- Upgrade to centos-6.6
- Change source from supermarket.getchef.com to supermarket.chef.io
- Alphabetize metadata in Berksfile
- Alphabetize metadata.rb
- Remove gostresql::client recipe in _centos.rb
- Remove 'PDD Done' message at end of default.rb
Added syntactical sugar to fix package installation

Turns out that package required do/end to work.  While I was there,
I noticed that cairocffi was spelled incorrectly so I fixed that.

Refs #6.
fix libffi-devel block; cleaned up .kitchen.yml
refs #6
Merge pull request #6 from osuosl-cookbooks/centos_refactor

Re-factor pgd_cookbook for Chef-CentOS