adds basic kitchen tests for postgresql cookbook

* basic bats tests for postgresql process
* added a few tests for configuration files (postgresql.conf and pg_hba.conf)
* added minimal Berkshelf file to manage apt dependency in test kitcken

I'm happy to add more tests (or adjust as needed).  Just wanted to make sure I pull requested while everything passes.

```
-----> Setting up <default-ubuntu-1204>...
Fetching: thor-0.18.1.gem (100%)
Fetching: busser-0.6.0.gem (100%)
Successfully installed thor-0.18.1
Successfully installed busser-0.6.0
2 gems installed
-----> Setting up Busser
       Creating BUSSER_ROOT in /tmp/busser
       Creating busser binstub
       Plugin bats installed (version 0.1.0)
-----> Running postinstall for bats plugin
      create  /tmp/bats20140206-3301-1gytv60/bats
      create  /tmp/bats20140206-3301-1gytv60/bats.tar.gz
Installed Bats to /tmp/busser/vendor/bats/bin/bats
      remove  /tmp/bats20140206-3301-1gytv60
       Finished setting up <default-ubuntu-1204> (0m9.08s).
-----> Verifying <default-ubuntu-1204>...
       Suite path directory /tmp/busser/suites does not exist, skipping.
Uploading /tmp/busser/suites/bats/verify_install.bats (mode=0644)
-----> Running bats test suite
 ✓ postgresql.conf file must exist
 ✓ pg_hba.conf file must exist
 ✓ postgres must reload cleanly

3 tests, 0 failures
```

There are a few things that food critic found but I will try to tackle those in a separate pull request (see http://acrmp.github.io/foodcritic/#FC015 and http://acrmp.github.io/foodcritic/#FC022 for more information)
```
postgresql [kitchen_tests]$ bundle exec foodcritic --epic-fail any ./
FC015: Consider converting definition to a LWRP: ./definitions/pg_database.rb:1
FC015: Consider converting definition to a LWRP: ./definitions/pg_database_extensions.rb:1
FC015: Consider converting definition to a LWRP: ./definitions/pg_user.rb:1
FC022: Resource condition within loop may not behave as expected: ./definitions/pg_database_extensions.rb:1
```