LU-847 quota: New quota tests to exercise accounting

LU-847 quota: New quota tests to exercise accounting

three tests are added in sanity-quota.sh:
- basic disk usage tracking for user & group;
- disk usage transfer for user & group;
- disk usage across restart for user & group;

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I605370db52f07875f725f48d7b0ce1bab9af80b3
Reviewed-on: http://review.whamcloud.com/1380
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>