Fix senlin help receiver-list
Fix senlin help receiver-list

There are problems for argparse to parse some metava formats. This patch
fixes the bug originated from this limitation when showing help for the
command 'receiver-list'.

Closes-Bug: #1550668
Change-Id: I973280766d3d0ac1a459293b1605368d8874b416

openstack/python-senlinclient,stackforge/python-senlinclient,stackforge/python-senlinclient,openstack/python-senlinclient