[TC] objcli.DeleteDirectory should work with Azure DataLake Gen 2

What is the problem?
In a customer issue, we found that DeleteDirectory will fail if the storage account is using Azure DataLake Gen 2. This is because IterateObjects includes directories in this setup and Azure will reject your request to delete a directory that is not empty

What is the solution?
On Azure we should change DeleteDirectory to handle this case. One idea would be to call DeleteDirectory recursively if ObjectAttrs.IsDir (once it has been fixed in MB-57910) and only then delete the directory object. If we did this we would have to be careful that other objects we are given may already have been deleted by the recursive call.