This introduces a new fs.Option flag, Sensitive and uses this along
with IsPassword to redact the info in the config file for support
purposes.
It adds this flag into backends where appropriate. It was necessary to
add oauthutil.SharedOptions to some backends as they were missing
them.
Fixes#5209
This includes an HDFS docker image to use with the integration tests.
Co-authored-by: Ivan Andreev <ivandeex@gmail.com>
Co-authored-by: Nick Craig-Wood <nick@craig-wood.com>