JCLOUDS-792: Configure chef-client security attributes

This commit also improves some internal behavior related to the
bootstrap configuration generation:

* Removes all methods that return the bootstrap DataBag or the raw
  configuration json to return the BootstrapConfig object instead.
* Deprecates all methods that provide support for old Chef versions.
* Formats the Enterprise Chef provider according to the jclouds
  formatting guidelines.
* Deprecates the ChefContext view. That view is not an abstraction and
  only provides access to the ChefService. It can be obtained from the
  ChefApi itself.