I actually have this exact WINRM configuration in my JSON.
"builders" : [{
"type": "azure-arm",
"client_id": "{{user `client_id`}}",
"client_secret": "{{user `client_secret`}}",
"subscription_id": "{{user `subscription_id`}}",
"tenant_id": "{{user `tenant_id`}}",
"managed_image_name" : "{{user `tag`}}",
"managed_image_resource_group_name" : "{{user `image_resource_group`}}",
"custom_managed_image_resource_group_name" : "{{user `image_resource_group`}}",
"custom_managed_image_name": "{{user `base_image`}}",
"build_resource_group_name" : "{{user `image_resource_group`}}",
"vm_size": "Standard_D4_v3",
"os_type": "{{user `os_type`}}",
"os_disk_size_gb": "{{user `disk_size`}}",
"communicator": "winrm",
"winrm_use_ssl": true,
"winrm_insecure": true,
"winrm_timeout": "10m",
"winrm_username": "packer"
}],
The Linux Build Agent running packer is timing out with these settings.