Ensure that members is a list
Ensure that members is a list

self.properties.get('members') should not be None.  Ensure that
an empty list is returned instead.

Change-Id: I01d191eafebac30ad25505b312ff6e936181bdbf
Closes-Bug: #1255697

srznew/heat,rh-s/heat,dragorosson/heat,openstack/heat,dims/heat,maestro-hybrid-cloud/heat,redhat-openstack/heat,cwolferh/heat-scratch,miguelgrinberg/heat,dims/heat,takeshineshiro/heat,cwolferh/heat-scratch,openstack/heat,redhat-openstack/heat,srznew/heat,jasondunsmore/heat,pshchelo/heat,maestro-hybrid-cloud/heat,jasondunsmore/heat,ntt-sic/heat,pratikmallya/heat,steveb/heat,cryptickp/heat,dragorosson/heat,gonzolino/heat,takeshineshiro/heat,miguelgrinberg/heat,NeCTAR-RC/heat,rh-s/heat,pratikmallya/heat,steveb/heat,cryptickp/heat,NeCTAR-RC/heat,noironetworks/heat,noironetworks/heat,pshchelo/heat,ntt-sic/heat,gonzolino/heat,rdo-management/heat,rdo-management/heat