LU-8264 lod: lfs setstripe fix for pool.

LU-8264 lod: lfs setstripe fix for pool.

If a file is created (with lfs) in the directory associated
with pool without -p pool_name option then limit stripe count
to number of osts in the pool as that directory is associated
with the pool. This patch fixes this problem.

Also removed the wrong check from ost-pools.sh, test_20 where
we were creating file in a directory associated with pool and
checking it as not part of the pool.

Add test cases in ost_pool.sh test_20.

Signed-off-by: Rahul Deshmukh <rahul.deshmukh@seagate.com>
Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Seagate-bug-id: MRP-3615
Change-Id: Id6dd5126856db7fc773a1fe9c837a214db8d6d70
Reviewed-on: https://review.whamcloud.com/20849
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>