Similar to file OST object allocation, introduce directory stripe
allocation by space usage, but they don't share the same code because
of the many differences between them: file has mirrors, PFL, object
precreation; while for directory, the first stripe is always on the
same MDT where its master object is on. The changes include:
* add lod_mdt_alloc_qos() to allocate stripes by space/inode usage.
* add lod_mdt_alloc_rr() to allocate stripes round-robin.
* add lod_mdt_alloc_specific() to allocate stripes in the old way.
* add sysfs support for lmv_desc field in LOD structure, and move
  those remain in procfs to sysfs.

This patch also changes LMV QoS code:
* mkdir by QoS if user mkdir by command 'lfs mkdir -i -1 ...', or the
  parent directory default LMV starting MDT index is -1.
* with the above change, 'space' hash flag is useless, remove all
  related code.
* previously 'lfs mkdir -i -1' QoS code is in lfs_setdirstripe(),
  but now it's done in LMV, remove the old code.

Update sanity 413a 413b to support QoS mkdir of both plain and
striped directories.

Update lfs-setdirstripe man to reflect the changes.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I8f5f8e46faae68ffd9a49a4ac1d450e951e979c5
Reviewed-on: https://review.whamcloud.com/35825


Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>