Support AKS Virtual Nodes

[patst]

Support for the AKS virtual nodes feature currently in preview (https://docs.microsoft.com/en-us/azure/aks/virtual-nodes-cli ).

The corresponding issue is #2508

I updated the docs and created an integration test.

I could use some help getting the test running. At the moment it fails with:

TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run=TestAccAzureRMKubernetesCluster_addonProfileAciConnectorLinux -timeout 180m -ldflags="-X=github.com/terraform-providers/terraform-provider-azurerm/version.ProviderVersion=acc"
?       github.com/terraform-providers/terraform-provider-azurerm       [no test files]
=== RUN   TestAccAzureRMKubernetesCluster_addonProfileAciConnectorLinux
=== PAUSE TestAccAzureRMKubernetesCluster_addonProfileAciConnectorLinux
=== CONT  TestAccAzureRMKubernetesCluster_addonProfileAciConnectorLinux
--- FAIL: TestAccAzureRMKubernetesCluster_addonProfileAciConnectorLinux (800.89s)
    testing.go:538: Step 0 error: After applying this step and refreshing, the plan was not empty:
        
        DIFF:
        
        UPDATE: azurerm_subnet.test-aci
          delegation.#:                                "1" => "0"
          delegation.0.name:                           "aciDelegation" => ""
          delegation.0.service_delegation.#:           "1" => "0"
          delegation.0.service_delegation.0.actions.#: "1" => "0"
          delegation.0.service_delegation.0.actions.0: "Microsoft.Network/virtualNetworks/subnets/action" => ""
          delegation.0.service_delegation.0.name:      "Microsoft.ContainerInstance/containerGroups" => ""
        
        STATE:
        ...

Any ideas why? It seems the Virtual Node plugins modifies the subnet config.

[tombuildsstuff]

hey @patst

Thanks for this PR :)

I've taken a look through and left some comments inline but this mostly LGTM - the test is failing because AKS is modifying the Subnet being passed in, so the configuration doesn't match the one provided by Azure - so if we can add in the missing configuration (and fix up the other minor comments) this should otherwise be good 👍

Thanks!

[patst]

Thanks for the fast review and the hint how to fix the testcase!
It is working now and I think all review comments are addressed.

[tombuildsstuff]

hey @patst

Thanks for pushing those changes - this now LGTM 👍

Thanks!

[tombuildsstuff]

Ignoring an Azure API timeout error (on destroying the resource) - the tests pass:

[tombuildsstuff]

Data Source tests pass too 👍

[ghost]

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