1167 Guesser: use index scan queries
1167 Guesser: use index scan queries

Modify the guesser sampling code in order to use index scan queries
instead of seq scan.

splashblot/dronedb,CartoDB/cartodb,codeandtheory/cartodb,splashblot/dronedb,raquel-ucl/cartodb,nyimbi/cartodb,splashblot/dronedb,dbirchak/cartodb,nuxcode/cartodb,splashblot/dronedb,thorncp/cartodb,thorncp/cartodb,future-analytics/cartodb,nyimbi/cartodb,CartoDB/cartodb,raquel-ucl/cartodb,dbirchak/cartodb,nyimbi/cartodb,UCL-ShippingGroup/cartodb-1,CartoDB/cartodb,codeandtheory/cartodb,dbirchak/cartodb,future-analytics/cartodb,DigitalCoder/cartodb,bloomberg/cartodb,codeandtheory/cartodb,thorncp/cartodb,DigitalCoder/cartodb,DigitalCoder/cartodb,DigitalCoder/cartodb,UCL-ShippingGroup/cartodb-1,nyimbi/cartodb,thorncp/cartodb,raquel-ucl/cartodb,DigitalCoder/cartodb,future-analytics/cartodb,raquel-ucl/cartodb,thorncp/cartodb,bloomberg/cartodb,UCL-ShippingGroup/cartodb-1,bloomberg/cartodb,codeandtheory/cartodb,nuxcode/cartodb,bloomberg/cartodb,UCL-ShippingGroup/cartodb-1,UCL-ShippingGroup/cartodb-1,CartoDB/cartodb,dbirchak/cartodb,CartoDB/cartodb,bloomberg/cartodb,raquel-ucl/cartodb,future-analytics/cartodb,codeandtheory/cartodb,splashblot/dronedb,dbirchak/cartodb,future-analytics/cartodb,nuxcode/cartodb,nuxcode/cartodb,nyimbi/cartodb,nuxcode/cartodb