Deployment will fail for cluster using user assigned identity when identity service is throttled

[norshtein]

Describe the bug
If the k8s cluster uses user assigned managed identity, in AKS-Engine generated template, the VM will not add the identity to its dependsOn:

    "resources": [
        {
            "type": "Microsoft.ManagedIdentity/userAssignedIdentities",
            "apiVersion": "[variables('apiVersionManagedIdentity')]",
            "name": "[variables('userAssignedID')]",
            "location": "[variables('location')]"
        },
        {
            "type": "Microsoft.Compute/virtualMachines",
            "apiVersion": "[variables('apiVersionCompute')]",
            "name": "[concat(variables('nodepool1VMNamePrefix'), copyIndex(variables('nodepool1Offset')))]",
            "location": "[variables('location')]",
            "dependsOn": [
                "[concat('Microsoft.Network/networkInterfaces/', variables('nodepool1VMNamePrefix'), 'nic-', copyIndex(variables('nodepool1Offset')))]",
                "[concat('Microsoft.Compute/availabilitySets/', variables('nodepool1AvailabilitySet'))]"
            ],
            "identity": {
                "type": "UserAssigned",
                "userAssignedIdentities": {
                    "[variables('userAssignedIDReference')]": {}
                }
            },
            ...

Normally it's OK because the creation of the identity is really fast, but when identity service is throttled(limitation is 8 requests per second per tenant according to identity team), the creation of identity will be slow and the deployment will fail because it tries to associate an non-existing identity to VM. The identity will be created finally but the deployment is early failed when trying to create VM.

Steps To Reproduce

Not always reproduce. Can only be reproduced for cluster using user assigned identity when identity service is throttled in tenant.

Expected behavior
The deployment should success.
AKS Engine version
All version.
Kubernetes version
All version.
Additional context

[norshtein]

/assign @norshtein

[stale]

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