Aggregation tests: Enable mapnik and rework the complete cells test
Aggregation tests: Enable mapnik and rework the complete cells test

Before it used to test exact tiles, now it test that if a cell/value is included
it will contain exactly the features that we expect

CartoDB/Windshaft-cartodb,CartoDB/Windshaft-cartodb,CartoDB/Windshaft-cartodb,CartoDB/Windshaft-cartodb