LU-3531 mdt: delete striped directory

Add delete striped directory, it includes

1. enable sync log between MDTs, so slave objects will
be delete by unlink log, which is similar as deleting ost
object.

2. retrieve layout information of striped directory on MDT,
then lock all of the slave objects before unlink.

3. remove a few unnecessary cfs_size_round, because update_size
and update_buf_size already do size_around inside.

4. add sanity 300 for striped dir test

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ib461156bbff9e416ac9d2500a0b9491427542340
Reviewed-on: http://review.whamcloud.com/7445
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>