Specifying multiple VM extensions in apimodel causes occasional deployment failures

[marosset]

Describe the bug
Specifying multiple VM extensions in an apimodel can cause random deployment failures.

We are seeing frequently on the sig-windows k8s test passes with the following apimodel/deployment template:
https://github.com/kubernetes-sigs/windows-testing/blob/master/job-templates/kubernetes_release_1_17.json

The deployments fail with the following error:
W1203 14:18:21.338] 2019/12/03 14:18:21 main.go:319: Something went wrong: starting e2e cluster: error creating cluster: cannot deploy: cannot get the create deployment future response: 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":"Conflict","message":"{\r\n "status": "Failed",\r\n "error": {\r\n "code": "ResourceDeploymentFailure",\r\n "message": "The resource operation completed with terminal provisioning state 'Failed'.",\r\n "details": [\r\n {\r\n "code": "DeploymentFailed",\r\n "message": "At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/DeployOperations for usage details.",\r\n "details": [\r\n {\r\n "code": "Conflict",\r\n "message": "{\r\n \"error\": {\r\n \"code\": \"Conflict\",\r\n \"message\": \"The request failed due to conflict with a concurrent request. \"\r\n }\r\n}"\r\n }\r\n ]\r\n }\r\n ]\r\n }\r\n}"}]

Example:
https://prow.k8s.io/view/gcs/kubernetes-jenkins/logs/ci-kubernetes-e2e-aks-engine-azure-1-17-windows/1201856259427405824

Expected behavior
Deployments do not fail

AKS Engine version
latest

Kubernetes version
any

Additional context

[marosset]

It looks like ARM is not happy having 3 different extensions (billing extension, master_extension, and gmsa-coredns extension) having deponsOn relationships with the cse-master-* extension and is throwing conflicts when processing the ARM template.

I tried to create a VM with multiple extensions through the Azure portal and noticed that the first extension had a deponsOn relationship on the vm and each additional extension had a depondsOn relationship to the previous extension.

I'm trying to get guidance from the ARM team and/or compute RP team to verify this is the cause.