LU-8152 utils: improve “lfs df” to show device status

LU-8152 utils: improve “lfs df” to show device status

This patch improves “lfs df” to check OS_STATE_* flags,
and show the device status as follows:

D stands for OS_STATE_DEGRADED
R stands for OS_STATE_READONLY
S stands for OS_STATE_ENOSPC
I stands for OS_STATE_ENOINO

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: Ic7389d935f1258bc4217dfe36fcbf2b468b14f20
Reviewed-on: https://review.whamcloud.com/23330
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>