Merge pull request #15657 from anvial/JUJU-3842-fix-deploy-aks-clean-…

…up-stage

#15657

This PR adds an explicit definition that deploy_aks used the `k8s` bootstrap provider. That will avoid errors on clean-up stage.

## Checklist

- [x] Code style: imports ordered, good names, simple structure, etc
- [x] Comments saying why design decisions were made
- [x] Go unit tests, with comments saying what you're testing

## QA steps


```sh
cd tests
./main.sh -v deploy_aks
```

tests/suites/deploy_aks/task.sh

@@ -16,10 +16,12 @@ test_deploy_aks() {
 	az aks create -g "${resource_group_name}" -n aks-cluster --generate-ssh-keys
 	juju add-k8s --aks --client --resource-group "${resource_group_name}" --storage test-aks-storage --cluster-name aks-cluster aks-k8s-cloud
 
+	export BOOTSTRAP_PROVIDER=k8s
 	bootstrap_custom_controller "test-deploy-aks" "aks-k8s-cloud"
 
 	test_deploy_aks_charms
 
+	export KILL_CONTROLLER=true
 	destroy_controller "test-deploy-aks"
 
 	juju remove-k8s --client aks-k8s-cloud