Before this change, for some operations, eg rcat or copyto (of a file)
rclone would attempt to create the container when using a SAS URL
limited to a container.
After this change we assume the container does not need creating when
using a container SAS URL.
See: https://forum.rclone.org/t/rclone-rcat-azure-blob-container-sas-token-403-error/16286