[COOK-2905] - use platform_family everywhere

We had platform_family used in some places, but not others. This
commit makes its use ubiquitous. It also shores up some gaps related
to cross-platform test coverage (kitchen.yml, tests).

* Add Debian to kitchen.yml
* Require omnibus across all test boxes
* Update README for Chef required version
* Switch minitest tests to use shellout
* Make a helper module for minitest
* Don't use a case statement for windows, its install flavor is...
  windows, just include that.
* Use platform_family across openjdk recipe