Replace old MinitTest framework with ChefSpec

This PR is mostly for Code Review purposes. I plan to add more coverage for other recipes as time permits. This is my first go at implementing ChefSpec for a few of the recipes in the postgresql cookbook. There are more complex recipes which should be tested, and for the most part I am just basically adding line coverage -- this said, there are some test which may not add much value, but were quick to write; and others which I would like more eyes on.

The ones which I would appreciate the most critical feedback are those which use various forms of conditionals in the examples. I struggled with this for a bit and finally got it the tests to pass, but I would like to get some eyes on them to ensure they are correctly testing the cookbook, opposed to running a useless test.

Any feedback would be greatly appreciated.