LU-12130 lod: make pool inheritance policy more consistent

LU-12130 lod: make pool inheritance policy more consistent

If directory's striping includes pool info, setstriping behaves
differently in relation to pool inheritance:
- if setstriping non-PFL layout the pool is inherited
- otherwise, it is not

Make inheritance policy consistent:
- when specified PFL does not include pool information - embed current
  pool specification into new layout

sanity.sh:test_65n is modified to illustrate the case.

HPE-bug-id: LUS-7180
Signed-off-by: Vladimir Saveliev <vlaidimir.saveliev@hpe.com>
Change-Id: I92b415e18ba7aadd2059da702878905249dd33c3
Reviewed-on: https://review.whamcloud.com/34536
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>