LU-129 Skip quotacheck on administratively disabled OSTs

LU-129 Skip quotacheck on administratively disabled OSTs

- skip quotacheck on administratively disabled OSTs.
- introduce OBD_NOTIFY_DEACTIVATE & OBD_NOTIFY_ACTIVATE event, thus lov is now aware of
  administratively enable/disable import event, and is able to udpate the 'ltd_activate'
  accordingly.

Issue: LU-129
Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I6af7dc09226d610bb1d481609a0a0ae09a05410e
Reviewed-on: http://review.whamcloud.com/387
Tested-by: Hudson
Reviewed-by: Oleg Drokin <green@whamcloud.com>