LU-14156 utils: mirror split to check for last in-sync early

LU-14156 utils: mirror split to check for last in-sync early

currently this check to prevent last in-sync component is done
once the file is open with O_RDWR which interrupts on-going
resync/extend process. instead we can do this check early once
the layout is fetched (after the first open with O_RDONLY).

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Iee08d23008b44d2a7b2127358116a95ace40b7dd
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/40782
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>