LU-12473 llapi: fix pool_list by path

LU-12473 llapi: fix pool_list by path

lfs/lctl pool_list <fs_path> would print the FS path as pool prefix.
print fsname properly instead.

Fixes: 8813fdf2a4f2 ("LU-5030 util: migrate liblustreapi to use cfs_get_paths()")
Change-Id: I016b794fabd3d161d4651b41989637aebdf31f36
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Reviewed-on: https://review.whamcloud.com/35320
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Reviewed-by: Oleg Drokin <green@whamcloud.com>