LU-14468 utils: improve 'lfs rmfid' error messages

LU-14468 utils: improve 'lfs rmfid' error messages

In lfs_rmfid_and_show_errors(), convert the error messages printed by
'lfs rmfid' from the format
  rmfid([0x20001a9f5:0x159:0x0]): rc = -39
to
  lfs rmfid: cannot remove [0x20001a9f5:0x155:0x0]: Directory not empty

Simplify the logic and swap rc and rc2 to follow conventions.

Lustre-commit: 6560ae08a788b3779118640837f68b499a99ee8c
Lustre-change: https://review.whamcloud.com/41727

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Iccd9e1054ed8842fc4f65dd601077cfdeaa1320c
Reviewed-on: https://review.whamcloud.com/41727
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/43452
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>