Add basic minitest tests to the Test Kitchen setup

Up until now, the Test Kitchen setup would only fail if a step in the process of converging the machine failed. This pull request added a few basic tests to the Test Kitchen workflow to ensure that Riak was installed and is functional.

**Note**: Tests are currently passing on Ubuntu and failing on CentOS due to the issue resolved in: https://github.com/basho/node_package/pull/51. It may be worth holding off on merging this until we can test with the fixed applied to the packages.