LU-3460 quota: don't schedule adjust when qsd stopped

LU-3460 quota: don't schedule adjust when qsd stopped

When the qsd is stopped, we should not schedule quota adjust or
index update anymore, because the writeback thread has been stopped,
and those scheduled requests will never be processed.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I33e0bbc7eb22be8a7edbc031f36ceff666575ebe
Reviewed-on: http://review.whamcloud.com/6731
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>