Cleaning up some provisioning warnings

[tyler-ball]

Fixes warnings like #95

[2016-07-28T11:34:40-06:00] WARN: Default value nil is invalid for property encrypt of resource chef_data_bag_item. Possible fixes: 1. Remove 'default: nil' if nil means 'undefined'. 2. Set a valid default value if there is a reasonable one. 3. Allow nil as a valid value of your property (for example, 'property :encrypt, [ String, nil ], default: nil'). Error: Property encrypt must be one of: true, false!  You passed nil. at /Users/tball/github/cheffish/lib/chef/resource/chef_data_bag_item.rb:189:in `new_encrypt'

\cc @jkeiser @chef/provisioning

[stuartpreston]

👍

[jjasghar]

🍧 and