Stop delete polling after status == DELETED.
Stop delete polling after status == DELETED.

A rackspace server can be in status DELETED for some minutes
until a 404 is raised. This change speeds the deletion of a stack
by considering the resource deleted as soon as the status changes
to DELETED.

Change-Id: Id81d3099ef6b41b374973074b065b20c2acc9667

JioCloud/heat,ntt-sic/heat,rdo-management/heat,takeshineshiro/heat,citrix-openstack-build/heat,openstack/heat,openstack/heat,pratikmallya/heat,rickerc/heat_audit,NeCTAR-RC/heat,noironetworks/heat,cryptickp/heat,srznew/heat,dims/heat,NeCTAR-RC/heat,steveb/heat,citrix-openstack-build/heat,rh-s/heat,steveb/heat,gonzolino/heat,miguelgrinberg/heat,dims/heat,noironetworks/heat,takeshineshiro/heat,gonzolino/heat,dragorosson/heat,pshchelo/heat,rh-s/heat,pratikmallya/heat,rdo-management/heat,ntt-sic/heat,dragorosson/heat,varunarya10/heat,miguelgrinberg/heat,srznew/heat,redhat-openstack/heat,pshchelo/heat,maestro-hybrid-cloud/heat,rickerc/heat_audit,jasondunsmore/heat,JioCloud/heat,redhat-openstack/heat,jasondunsmore/heat,cwolferh/heat-scratch,maestro-hybrid-cloud/heat,cwolferh/heat-scratch,varunarya10/heat,cryptickp/heat