Fix `to_boolean` in cfn_helper
Fix `to_boolean` in cfn_helper

The lowercase conversion and striping whitespace from strings was being ignored.

Signed-off-by: Tomas Sedovic <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@sedovic.cz>

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