Display error message on invalid template URL
Display error message on invalid template URL

Fixes #19

Triv90/Heat,dragorosson/heat,Triv90/Heat,noironetworks/heat,ntt-sic/heat,miguelgrinberg/heat,maestro-hybrid-cloud/heat,dims/heat,pshchelo/heat,openstack/heat-cfntools,steveb/heat,rdo-management/heat,rickerc/heat_audit,NeCTAR-RC/heat,openstack/heat,citrix-openstack-build/heat,ntt-sic/heat,cwolferh/heat-scratch,redhat-openstack/heat,dragorosson/heat,pratikmallya/heat,dims/heat,bbandaru/heat-cfntools,gonzolino/heat,takeshineshiro/heat,NeCTAR-RC/heat,gonzolino/heat,sdake/heat-jeos,miguelgrinberg/heat,rh-s/heat,rickerc/heat_audit,jasondunsmore/heat,steveb/heat-cfntools,rh-s/heat,varunarya10/heat,JioCloud/heat,maestro-hybrid-cloud/heat,pratikmallya/heat,varunarya10/heat,openstack/heat,JioCloud/heat,cryptickp/heat,Triv90/Heat,noironetworks/heat,redhat-openstack/heat,steveb/heat,cwolferh/heat-scratch,jasondunsmore/heat,pshchelo/heat,takeshineshiro/heat,cryptickp/heat,srznew/heat,steveb/heat-cfntools,srznew/heat,citrix-openstack-build/heat,rdo-management/heat