Instead on relying on the isPrimaryMeterRegion attribute in prices returned by the Azure API, use whatever price is returned for that instance type & region with the latest effectiveStartDate
This is required as some instance types don't have any primary price entry returned (for reasons unknown), so otherwise may be missed
Aims to resolve #5
isPrimaryMeterRegion
attribute in prices returned by the Azure API, use whatever price is returned for that instance type & region with the latesteffectiveStartDate