* 'class' is equivalent to inst.__class__.__name__
* renamed 'update_all_keys' to '_update_key_for_nodes' because it really updates 1 key for all nodes
    - added _ to make it a 'protected' member, since it can be dangerous depending which key is updated
* added 'update_labels' to specifically update labels
    - special case of _update_key_for_nodes
    - the only one used in the code
* removed default argument for format_node method
    - make caller more responsible of what he wants to format
    - makes code more readable
* moved subprocess import on top of the file
* removed unused method: '.get_node_name'
* replaced 'hasattr' with try...except (better to ask forgiveness than permission)
* renamed 'name' to 'key' in for loop, not to confuse with name attribute
    - makes code more readable