Azure Blob Storage: download_to does not work for containers where blobs folders and files with the same name

[pjbull]

In azure blob storage you can have the following situation:

• az://container/hello # a file on storage
• az://container/hello/world # different file on storage

In this case, az://container/hello is both a file and a folder. At the very least, this breaks our download_to method, since it is recursive only if is_file returns False, which will never happen.