Fix "members" property check
Fix "members" property check

According to https://bugs.launchpad.net/heat/+bug/1247638/comments/3

Closes-Bug: #1248571
Closes-Bug: #1247638
Change-Id: I4a61963d730250d8c3714b20c9cc7bb3717d85af

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