Verify additional Duo authentication methods work

[mnlevy1981]

With #51 I think this will work as well, but I didn't test it as part of that PR... Duo can be configured to prompt

Rather than wait for a user to tell us this does / doesn't work, it doesn't seem too difficult to spin up a VM and test it. (If it doesn't work, it would probably require an upstream fix in Paramiko.)