Don't send multiple update-cancel messages to an event
Don't send multiple update-cancel messages to an event

Change-Id: Ib64da11ed5584c1a2eef98378d3201a6949fac7d
Closes-Bug: #1376900
(cherry picked from commit 75242b9c67aafa80b4d4a13cfae6c50ba7f85b79)

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