Made kitchen actually run the minitest chef specs.

While working on the container_action :create PR, I found that the kitchen specs are not run (which is why checking that a test fail before adding code is a good practice). The reason is that the `recipe[minitest-handler]` should be in the run_list of the different suites in .kitchen.yml

This PR does the following:
 - add `recipe[minitest-handler]` at the end the run_list of every suite defined in `.kitchen.yml`
 - rename `files/default/test/minitest/*_test.rb` to `files/default/test/*_test.rb` (the old location has been deprecated since version 0.1.8 of the [minitest-handler-cookbook](https://github.com/btm/minitest-handler-cookbook))
 - fix a few typos in recipe describes

I didn't try to make the specs pass (too many suites for my slow Internet) but at least make it so that the specs can run.