Add commands of clustering service to doc
Add commands of clustering service to doc

This patch adds the 'objects'/'resources' provided by the clustering
service (senlin) to the commands doc.

Change-Id: I028bd919f5b357d1b6e806c85e83a1a63c42839c

dtroyer/python-openstackclient,openstack/python-openstackclient,redhat-openstack/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient