Qa/delete node

#### Reviewers
@hmunfru @alberts-tid 

#### Description
 ADD Acceptance tests: 'Delete node' API resource
I have prefered to manage this exception there because TCs will validate only if the result is None (I am interested in the error) instead of manage the exception in each TC. TCs have something like this:
    response = get_chef_node_info_from_server(world.node_name)
    assert_equals(response, None, "Node has not been unregister from Chef-Server")