* Fix Kubernetes API auth regression from 393e43b8
Commit 393e43b8 renames url_username and url_password to username and
password, which breaks authentication to a Kubernetes API endpoint as
fetch_url() in ansible.module_utils.urls relies on url_username and
url_password being set.
* Add aliases for clustering/kubernetes.py
- username as alias for url_username
- password as alias for url_password
026dc4f957