message: Add missing properties for Vmss zone GA
diff: "singlePlacementGroup": {
  "type": "boolean",
  "description": "When true this limits the scale set to a single placement group, of max size 100 virtual machines."
  + },
  + "zoneBalance": {
  + "type": "boolean",
  + "description": "Whether to force stictly even Virtual Machine distribution cross x-zones in case there is zone outage."
  + },
  + "platformFaultDomainCount": {
  + "type": "integer",
  + "format": "int32",
  + "description": "Fault Domain count for each placement group."
  }
  },
  "description": "Describes the properties of a Virtual Machine Scale Set."
  