The race detector currently detects a race with len(chan) against
close(chan).
See: https://github.com/golang/go/issues/27070
Skip the tests which trip this bug under the race detector.
The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.
The new code layout is documented in CONTRIBUTING.