o Export disk time and sector used by a group to user space through cgroup
  interface.

o Also export a "dequeue" interface to cgroup which keeps track of how many
  a times a group was deleted from service tree. Helps in debugging.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>