A node's attributes says it is a kind_of? Hash, but does not support all Hash methods

Consider the following session from shef console:

chef > anode = nodes.all.first;true
=> true
chef > anode.attribute.kind_of? Hash
=> true
chef > anode.attribute.keys
=> ["nested", "tag", "value", "multi_word"]
chef > anode.attribute.delete("tag")
=> "tag"
chef > anode.attribute.keys
=> ["delete", "nested", "tag", "value", "multi_word"]
chef >

We should at least add support for easily deleting attributes. Ideally, if node.attribute is going to say it is a kind of Hash, then it should implement all Hash methods – or at least raise an exception for unsupported operations.