Fix "openstack cluster policy binding list <cluster>"
Fix "openstack cluster policy binding list <cluster>"

Before this patch,"openstack cluster policy binding list <cluster>"
will list nothing.

Change-Id: Ife35efd28af8207d6dfbc077dd70550c76ab565d

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