Update to include few duo features

Feature credential process

Always return the same number of values from _initiate_authentication()

Ask for authentication method if there is no default method set in Du…

…o Security settings

support for non-public AWS regions (e.g. GovCloud)

Change `AuthMethod` parameter to `FormsAuthentication`

fixing username and password disclosure and

authentication with cookies on non-windows system

Default SSPI to True on Windows only, False otherwise

dropped botocore dependency

pdecat: Document new libkrb5-dev system dependency for pykerberos