Active Directory configuration fails when processing DSC Extension "CreateADForest"

[active-directory-new-domain-ha-2-dc](https://github.com/Azure/azure-quickstart-templates/tree/master/active-directory-new-domain-ha-2-dc)

### Issue Details
Deployment fails when processing DSC Extension CreateADForest.

Full Error Text:
{ "status": "Failed", "error": { "code": "ResourceDeploymentFailure", "message": "The resource operation completed with terminal provisioning state 'Failed'.", "details": [ { "code": "VMExtensionProvisioningError", "message": "VM has reported a failure when processing extension 'CreateADForest'. Error message: \"DSC Configuration 'CreateADPDC' completed with error(s). Following are the first few: Interface \"Ethernet\" is not available. Please select a valid interface and try again. PowerShell DSC resource MSFT_xDNSServerAddress failed to execute Test-TargetResource functionality with error message: The running command stopped because the preference variable \"ErrorActionPreference\" or common parameter is set to Stop: No matching MSFT_DNSClientServerAddress objects found by CIM query for instances of the ROOT/StandardCimv2/MSFT_DNSClientServerAddress class on the CIM server: SELECT * FROM MSFT_DNSClientServerAddress WHERE ((InterfaceAlias LIKE 'Ethernet')) AND ((AddressFamily = 2)). Verify query parameters and retry. The SendConfigurationApply function did not succeed.\"." } ] } }

### Repro steps
1. Deploy Template with all the defaults to West US, just adding values for required fields.
2. Error encountered after about 5 minutes.

Start with the active-directory-new-domain-ha-2-dc template linked in the issue and the CreateADForest DSC extension configuration. Reproduce the default deployment in West US, then investigate why the xDNSServerAddress query cannot find the Ethernet interface. Done means the template deploys successfully without the reported extension error.

Written by the indexing model from the issue text.