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

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

* In ost-pool.sh, reset $MOUNT's stripe offset, so that the created
  directory 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

Lustre-change: https://review.whamcloud.com/43882
Lustre-commit: TBD (from c82f557324bc0048c308d1a2135699e7c83169e1)

Test-Parameters: trivial testlist=replay-single,ost-pools
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Idf6884faf1271a3864710aeab0ba0eca154bf492
Reviewed-on: https://review.whamcloud.com/43976
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>