LU-14448 lod: verify LOV before set/inherit

LU-14448 lod: verify LOV before set/inherit

DoM layout can only be set as entry in composite layout, and its
stripe count should always be 0.

Verify LOV before setting and inheriting.

Add sanity 270i.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I016d1a202960bfebc72dd808de5f80e09051a01e
Reviewed-on: https://review.whamcloud.com/45039
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>