LU-847 quota: client retrieve quota usage directly

LU-847 quota: client retrieve quota usage directly

Current 'lfs quota' sends getquota RPC to MDS, and MDS is responsible
for retrieving disk usage from all targets, this scheme will be
changed to client retrieving disk usage from all targets directly.

This patch addresses the compatibility issue as well: If the getquota
returned by MDS has QIF_SPACE, client just trust the disk usage
returned by MDS, otherwise, client has to issue RPCs to all OSTs to
collect disk usage by itself.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: Ia94d3b3ba280d5b31d2d3c508412d662f4e95321
Reviewed-on: http://review.whamcloud.com/1382
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>