rds-deployment-existing-ad RDSDeployment DSC Config Error

azure-quickstart-templates/application-workloads/rds/rds-deployment-existing-ad/
https://github.com/Azure/azure-quickstart-templates/tree/master/application-workloads/rds/rds-deployment-existing-ad

### Issue Details

Error creating the RDS Farm (server pool). Extensions for cb-vm (broker) show "provisioning failed." When I log into cb-vm Remote Desktop Services in server manager shows "A remote Desktop Services deployment does not exist in the server pool"

{"code":"DeploymentFailed","message":"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/DeployOperations for usage details.","details":[{"code":"VMExtensionProvisioningError","message":"VM has reported a failure when processing extension 'rdsdeployment'. Error message: \"DSC Configuration 'RDSDeployment' completed with error(s). Following are the first few: The RD Connection Broker cannot be joined to the RD Management server. Unable to add server BROKER.HOARLLC.LOC to the list of servers on the RD Connection Broker server BROKER.HOARLLC.LOC..Exception of type 'System.Runtime.InteropServices.COMException' was thrown. Exception of type 'Microsoft.RemoteDesktopServices.Common.RDManagementException' was thrown. Exception of type 'Microsoft.RemoteDesktopServices.Common.RDManagementException' was thrown.\"\r\n\r\nMore information on troubleshooting is available at https://aka.ms/VMExtensionDSCWindowsTroubleshoot "}]}

Attached logs from C:\WindowsAzure\Logs\Plugins\Microsoft.Powershell.DSC\2.83.1.0
[DSC Logs 2.83.1.0.zip](https://github.com/Azure/azure-quickstart-templates/files/7007960/DSC.Logs.2.83.1.0.zip)

Start with the rds-deployment-existing-ad template directory and inspect the attached DSC logs from C:\WindowsAzure\Logs\Plugins\Microsoft.Powershell.DSC\2.83.1.0. Trace the RDSDeployment failure involving the RD Connection Broker and RD Management server; done means the RDS Farm is created without the provisioning error and the deployment exists in Server Manager.

Written by the indexing model from the issue text.