Add test for CartoCSS error reporting on POST to layergroup
Add test for CartoCSS error reporting on POST to layergroup

UCL-ShippingGroup/Windshaft-cartodb,CartoDB/Windshaft-cartodb,CartoDB/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb,UCL-ShippingGroup/Windshaft-cartodb,CartoDB/Windshaft-cartodb,manueltimita/Windshaft-cartodb,CartoDB/Windshaft-cartodb,manueltimita/Windshaft-cartodb,manueltimita/Windshaft-cartodb