In pull request #4443, we renamed some of the Azure and S3 options to
use dashes '-' instead of underscores '_' for consistency. However, our
treatment of the options in the backend constructors still required that
the underscore versions be present even if the dashed version was
provided.
Now, we allow for either option to be present, but the value for the
dashed version will take precedence.
Kenneth Hsu
29f1d2c3cb