rc: fix --loopback with rc/list and others
rc: fix --loopback with rc/list and others

Before this change `rclone rc --loopback` would give the error "bad
JSON".

This was because the output of the `rc/list` command was not serialzed
through JSON.

This serializes it through JSON and fixes that (and probably other)
command.

ncw/rclone,ncw/rclone,ncw/rclone,ncw/rclone