Add option to force removing Dockerfile.stfubuntu

# Force removing stfubuntu docker image

if [ "$1" == "--force-stfubuntu" ]; then

    if [ -z `docker images -q stfubuntu` ]; then

        docker rmi --force `docker images -q stfubuntu` || exit 1

    fi

fi

# Check and build stfubuntu image

if [ -z `docker images -q stfubuntu` ]; then

    docker build --no-cache --tag stfubuntu:18.04 -f Dockerfile.stfubuntu --force-rm  . || exit 1