Use Lwt.choose to monitor the event loops
Use Lwt.choose to monitor the event loops

Lwt.join waits until *all* threads have failed before reporting a
problem, which is unhelpful.

Signed-off-by: Thomas Leonard <ea62ade398c3addd3bcc52285a00e98f3b0c618f@docker.com>

docker/datakit,docker/datakit,docker/datakit