fsadm fix for downsize of unmounted fs

fsadm fix for downsize of unmounted fs

Fix for the last commit as $MOUNTED is not only used as bool flag,
but also store mounted location for remount - so parsing output
from mount differently then from /proc/mounts.

Prefix calls of 'tunefs' tools with LANG=C to be sure we always do get
some nonlocalized strings.

Avoid using forced 'resize2fs' for cleanly unmounted filesystems and
run regular fsck -f for this case as required by resize2fs.

'fsadm check' uses date difference for extX filesystems between
the last mount and last check of 'fsck -f' execution and if the mount
was later run 'fsck' with -f so resize2fs is happy and user does not
need to pass '-f' flag.