Check for the presence of Metadat before trying to include it the multipart
Check for the presence of Metadat before trying to include it the multipart

Signed-off-by: Angus Salkeld <86b65304d27d8de73dd7d624c33df7e088f8d94b@redhat.com>

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