LU-11425 quota: support quota for DoM

LU-11425 quota: support quota for DoM

Support block quota enforcement on MDT to accommodate the data
writing introduced by DoM.

This patch adds a new qsd_instance on the OSD device at MDT to
implement the quota enforcement on block data, for there is only
one type of quota (meta data or block data) to be handled in one
qsd_instance in the current quota design of Lustre, it's much more
changes to adapt the qsd_instance to support more quota type than
to use a separated qsd_instance to enfore meta data on MDT.

Change-Id: I7c57f383d338cf0070e05ecc318d42586c39371e
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/33257
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>