Automated live test for Azure Container Instance managed identity

[chlowell]

See https://github.com/Azure/azure-sdk-for-go/pull/22652/files for an example

[chlowell]

Azure CLI now requires additional parameters to deploy ACI: https://github.com/Azure/azure-sdk-for-go/pull/23796/files

[chlowell]

It's no longer necessary to work around test subscription limitations with az container exec: Azure/azure-sdk-for-go#24151