IoTHub Dps API failed to parse error message when it failed to create iothub dps

After tested, I found iothub dps api would fail to parse error message when it failed to create iothub dps.

Http request:
```
PUT https://management.azure.com/subscriptions/xx-xx-xx-xx/resourceGroups/acctestRG-iothubdps-test01/providers/Microsoft.Devices/provisioningServices/IotHubTF-DPS-test01

{
"location": "eastus2",
"properties": {
"iotHubs": []
},
"sku": {
"name": "F1",
"capacity": 1
},
"tags": {}
}
```

Error message:

No file or test is named. Start by locating the IoT Hub DPS API specification and its create-resource error response definition, then compare it with the HTTP request and error shown in the issue. Done means the failed create request exposes the service error message instead of failing to parse it.

Written by the indexing model from the issue text.