Autodetect encrypted data bag items in data_bag_item dsl method.

OK, ready to go @opscode/client-engineers. This resolves https://github.com/opscode/chef/issues/1849.


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* :construction: Would like feedback on expected behavior @sersut @danielsdeleo @lamont-granquist :construction: 

Slightly confused here. Are we trying to filter `id` key in this hash? Maybe we can use [this](http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-reject) in that case.