"umountiscsi.sh" tries to unmount "/" root partition on "service open-iscsi stop" command if no block device assigned to iscsi device!

Whilst trying to debug open-iscsi on Trusty (because it doesn't appear to be allocating a block-device to iSCSI assocaitions out of the box - a separate issue), it became apparent that I could not simply stop the open-iscsi device because when you do, but when no block device is associated with the iscsi session, it tries to un-mount "/" and obviously fails:

shared iscsi # /etc/init.d/open-iscsi stop
 * Unmounting iscsi-backed filesystems umount: /: device is busy.
        (In some cases useful info about processes that use
         the device is found by lsof(8) or fuser(1))
 * Could not unmount /
                                                                                                                                                                                                                                                                          [fail]
invoke-rc.d: initscript umountiscsi.sh, action "stop" failed.
 * Couldn't unmount all iSCSI devices. Cannot stop iSCSI service

The script responsible for this it "umountiscsi.sh", and installed as part of the open-iscsi package, and is run on stop by the init script to try and unmount any iscsi volumes before pulling down the iscsi daemon.

The section of code responsible is this:
    for HOST_DIR in /sys/devices/platform/host*; do
        if ! [ -d $HOST_DIR/iscsi_host* ]; then
            continue
        fi
        for SESSION_DIR in $HOST_DIR/session*; do
                if ! [ -d $SESSION_DIR/target* ]; then
                        continue
                fi
                for BLOCK_FILE in $SESSION_DIR/target*/*\:*/block/*; do
                        BLOCK_DEV=`echo "$BLOCK_FILE" | sed 's/.*block\///'`
                        DOS_PARTITIONS="`awk "/^\/dev\/$BLOCK_DEV/ { print \\$2; }" < /proc/mounts`"
                        for DEVICE in $DOS_PARTITIONS; do
                                #log_progress_msg $DEVICE
                                #echo $DEVICE
                                umount $DEVICE
                                exit_status=$?
                                if ! [ $exit_status -eq 0 ]; then
                                        umount_fail=1
                                        log_warning_msg "Could not unmount $DEVICE"
                                fi
                        done
                done
        done
    done

I attach a very simple patch that fixes this - please include and push upstream.