Reduce the number of default assumptions

These changes reduce the number of default assumptions for a "skeleton" cookbook.

* Add CentOS to kitchen platforms to match default `kitchen init`
  behavior in test-kitchen 1.0
* Move apt recipe to ubuntu platform run list
* Remove `supports` from metadata
* Make the version sub-1.0, to accomodate development versions under
  semver
* Remove the package resource in the default recipe, and the related
  specs
* Use generalized default config in the spec_helper that is commented
  by default