LU-10350 lod: adjust stripe count to available ost count

LU-10350 lod: adjust stripe count to available ost count

* When user specifies -1 stripe count or more stripe count than the
  ost count of a pool, we'd adjust the stripe count otherwise we
  cannot alloc enough stripe objects, as LOD reports as follows:

  lod_alloc_specific() can't lstripe objid [obj_fid]: have %d want %u

  where %d is the ost count of a pool, and %u is the total ost count
  if user specifies -1 stripe count of a bigger stripe count value
  than %d as user specifies.

* In ost-pool.sh, reset $MOUNT's stripe offset, so that the created
  diretory will not inherit it from root directory.

* Preserve the root directory layout in replay-single (run before
  ost-pools) to avoid leaving a bad layout on the root dir.
  Lustre-change: https://review.whamcloud.com/43872

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Idf6884faf1271a3864710aeab0ba0eca154bf492