Allow Managed identity to be used for deploying and building images

[xpillons]

• allow a deployment to be done from a VM under a System Assigned Managed Identity
• add dependencies between ASG and VMs
• provide tenant_id and user_object_id as variables to fix an issue with the azurerm_client_config data provider when using Managed Identity
• Use managed identity for packer. No more need to use SPN and define an spn.json file
  close Allow deployment from a VM under Managed Identity #580
  close Error while destroying resources with Terraform #584
  close Unable to create resources with a system managed identity #582
  close use managed identity with Packer #569