Before this change `rclone about swift:container` would show aggregate
info about all the containers, not just the one in use.
This causes a problem if container listing is disabled (for example in
the Blomp service).
This fix makes `rclone about swift:container` show only the info about
the given `container`. If aggregate info about all the containers is
required then use `rclone about swift:`.
See: https://forum.rclone.org/t/rclone-mount-blomp-problem/29151/18