LU-15647 utils: 'lfs df' shouldn't loop forever

LU-15647 utils: 'lfs df' shouldn't loop forever

Don't loop forever in "lfs df" if there is a problem fetching
the target statfs information from the kernel and -ENODEV is
not returned for whatever reason.

Lustre-change: https://review.whamcloud.com/46813
Lustre-commit: 41703e9b5fe7061b313805384b08372d4fe82cec

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I5110c7246cf53eb5c4d59424a44b73b9d23ebbe5
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/47605
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>