AKS: add aks-custom-headers for nodepool and update

[andyzhangx]

---

This checklist is used to make sure that common guidelines for a pull request are followed.

General Guidelines

• Have you run azdev style <YOUR_EXT> locally? (pip install azdev required)
• Have you run python scripts/ci/test_index.py -q locally?

For new extensions:

• My extension description/summary conforms to the Extension Summary Guidelines.

About Extension Publish

There is a pipeline to automatically build, upload and publish extension wheels.
Once your PR is merged into master branch, a new PR will be created to update src/index.json automatically.
The precondition is to put your code inside this repo and upgrade the version in the PR but do not modify src/index.json.

Test result

• az aks nodepool add ... CustomizedUbuntu=aks-ubuntu-1804

# az aks nodepool add -g $RESOURCE_GROUP_NAME --cluster-name $CLUSTER_NAME --node-count 1 --kubernetes-version 1.15.10 --aks-custom-headers CustomizedUbuntu=aks-ubuntu-1804 -n andytest
The behavior of this command has been altered by the following extension: aks-preview
{
  "agentPoolType": "VirtualMachineScaleSets",
  "availabilityZones": null,
  "count": 1,
  "enableAutoScaling": null,
  "enableNodePublicIp": false,
  "id": "/subscriptions/xxx/resourcegroups/andy-aks11510/providers/Microsoft.ContainerService/managedClusters/andy-aks11510/agentPools/andytest",
  "maxCount": null,
  "maxPods": 110,
  "minCount": null,
  "mode": "User",
  "name": "andytest",
  "nodeLabels": null,
  "nodeTaints": null,
  "orchestratorVersion": "1.15.10",
  "osDiskSizeGb": 100,
  "osType": "Linux",
  "provisioningState": "Succeeded",
  "resourceGroup": "andy-aks11510",
  "scaleSetEvictionPolicy": null,
  "scaleSetPriority": null,
  "spotMaxPrice": null,
  "tags": null,
  "type": "Microsoft.ContainerService/managedClusters/agentPools",
  "vmSize": "Standard_DS2_v2",
  "vnetSubnetId": null
}

• az aks nodepool add ... (wrong aks-custom-headers format)

# az aks nodepool add -g $RESOURCE_GROUP_NAME --cluster-name $CLUSTER_NAME --node-count 1 --kubernetes-version 1.15.10 --aks-custom-headers CustomizedUbunt -n andytest2
The behavior of this command has been altered by the following extension: aks-preview
custom headers format is incorrect

• Without --aks-custom-headers

# az aks nodepool add -g $RESOURCE_GROUP_NAME --cluster-name $CLUSTER_NAME --node-count 1 --kubernetes-version 1.15.10 -n andytest2
The behavior of this command has been altered by the following extension: aks-preview
{
  "agentPoolType": "VirtualMachineScaleSets",
  "availabilityZones": null,
  "count": 1,
  "enableAutoScaling": null,
  "enableNodePublicIp": false,
  "id": "/subscriptions/xxx/resourcegroups/andy-aks11510/providers/Microsoft.ContainerService/managedClusters/andy-aks11510/agentPools/andytest2",
  "maxCount": null,
  "maxPods": 110,
  "minCount": null,
  "mode": "User",
  "name": "andytest2",
  "nodeLabels": null,
  "nodeTaints": null,
  "orchestratorVersion": "1.15.10",
  "osDiskSizeGb": 100,
  "osType": "Linux",
  "provisioningState": "Succeeded",
  "resourceGroup": "andy-aks11510",
  "scaleSetEvictionPolicy": null,
  "scaleSetPriority": null,
  "spotMaxPrice": null,
  "tags": null,
  "type": "Microsoft.ContainerService/managedClusters/agentPools",
  "vmSize": "Standard_DS2_v2",
  "vnetSubnetId": null
}

[azuresdkci]

If this PR is for a new extension or change to an existing extension, use the following to try out the changes in this PR:

docker run -it microsoft/azure-cli:latest
export EXT=<NAME>
pip install --upgrade --target ~/.azure/cliextensions/$EXT "git+https://github.com/andyzhangx/azure-cli-extensions.git@aks-custom-headers#subdirectory=src/$EXT&egg=$EXT"

[andyzhangx]

/hold

[andyzhangx]

cc @palma21

[palma21]

CC @zhedahht @xuto2 @gtxistxgao
Thanks @andyzhangx !

[yonzhan]

AKS

[andyzhangx]

PR is ready for review, thanks

[andyzhangx]

/assign @zhedahht @xuto2 @gtxistxgao @zqingqing1
can you take a review? thanks.