umountroot cannot handle fuse host mounts

Binary package hint: sysvinit

If root is loopmounted the host mount will be handled by the initrd and will not show up in fstab
Hence explicit DEV and TYPE are required. For fuse mounted hosts the TYPE in /proc/mounts is
fusblk so we need to rely on vol_id first to get the real filesystem type.

Following is the proposed code that should replace remount_ro within umountroot. We first
try to remount as usual and if that fails, we try to use explicit DEV and TYPE.

remount_ro () {
# ntfs-3g in hardy does not allow remounts (v 1.1120, gutsy v 1.913), and does not take -n why?
# use sed instead of awk: sed -n "\:^/[^ ]* $MTPT :p" /proc/mounts
 echo remounting $1
 local MTPT=$1
 [ "$VERBOSE" = no ] || log_action_begin_msg "Mounting $MTPT filesystem read-only"
 MOUNT_FORCE_OPT=
 [ "$(uname -s)" = "GNU/kFreeBSD" ] && MOUNT_FORCE_OPT=-f
 # This:
 # mount -n -o remount,ro /
 # will act on a bind mount of / if there is one.
 # See #339023 and the comment in checkroot.sh
 mount $MOUNT_FORCE_OPT -n -o remount,ro -t dummytype dummydev $MTPT 2>/dev/null \
 || mount $MOUNT_FORCE_OPT -n -o remount,ro dummydev $MTPT 2>/dev/null \
 || mount $MOUNT_FORCE_OPT -n -o remount,ro $MTPT 2>/dev/null
 ES=$?
 if [ $ES != 0 ]; then
  local MOUNT="$(sed -n "\:^/[^ ]* $MTPT :p" /proc/mounts)"
  local DEV=${MOUNT%% *}
  local TYPE=$(/lib/udev/vol_id -t $DEV 2> /dev/null)
  if [ -z "$TYPE" ]; then
   TYPE=${MOUNT#* $MTPT }
   TYPE=${TYPE%% *}
  fi
  mount $MOUNT_FORCE_OPT -n -o remount,ro -t $TYPE $DEV $MTPT 2>/dev/null || \
  mount $MOUNT_FORCE_OPT -o remount,ro -t $TYPE $DEV $MTPT
  ES=$?
 fi
 [ "$VERBOSE" = no ] || log_action_end_msg $ES
}