AWS and OpenStack should handle node metadata the same way.
Currently OS has ex_metadata argument for create_node while for AWS the user needs to call an additional function. Also there is not an unified way to get metadata.
- unify argument order in docstrings for create_node in both AWS & OS
- add ex_metadata argument to create_node for AWS (EC2)
- add ex_get_metadata_for_node to both drivers for AWS and OS