Add `scripts/runner.sh` as program starter for tests

#!/usr/bin/env bash

function help() {

  echo "Usage:"

  echo "  $(basename "$0") COMMAND"

  echo ""

  echo "  Where COMMAND is one of:"

  echo "    start PIDFILE PROGRAM ARGS...  Run PROGRAM and record its PID in PIDFILE"

  echo "    stop SIGNAL PIDFILE            Send SIGNAL to the PID contained in PIDFILE"

  echo "    help                      Print this message"

}

function readpid() {

  if [ $# -eq 0 ]; then

    echo "FATAL: readpid(): Missing pifile" >&2

    exit 1

  fi

  pidfile="$1"

  read -r pid <"$pidfile"

  echo $pid

}

function run() {

  if [[ -n "${RUNNER_SKIP_START}" && "${RUNNER_SKIP_START}" != "0" ]]; then

    exit 0

  fi

  if [ $# -eq 0 ]; then

    echo "FATAL: missing program pidfile" >&2

  elif [ $# -eq 1 ]; then

    echo "FATAL: missing program to run" >&2

    help

    exit 1

  fi

  pidfile="$1"

  shift

  if [ -e "$pidfile" ]; then

    pid=$(readpid "$pidfile")

    echo "$pid"

    if pgrep --pidfile "$pidfile"; then

      exit 1

    fi

  fi

  "$@" 2>runner.$$.err 1>runner.$$.out 0</dev/null &

  pid=$!

  echo $pid >"$pidfile"

  sleep 1

  if ! kill -0 $pid; then

    echo "Process $pid does not seem to exist." >&2

    echo "The program below may not exist or may have crashed while starting:" >&2

    echo "  $*" >&2

    echo " STDOUT: " >&2

    cat "runner.$$.out" >&2

    echo " STDERR: " >&2

    cat "runner.$$.err" >&2

    rm runner.$$.out runner.$$.err

    exit 1

  fi

  exit 0

}

function stop() {

  if [ $# -eq 0 ]; then

    echo "FATAL: missing signal" >&2

    exit 1

  elif [ $# -eq 1 ]; then

    echo "FATAL: missing pidfile" >&2

    exit 1

  fi

  signal="$1"

  pidfile="$2"

  if [ ! -e "$pidfile" ]; then

    echo "FATAL: pidfile '$pidfile' does not exist" >&2

    exit 1

  fi

  if pkill "-$signal" --pidfile "$pidfile"; then

    rm "$pidfile"

    rm runner.$$.out runner.$$.err

    exit 0

  fi

  exit 1

}

if [ $# -eq 0 ]; then

  echo "FATAL: missing arguments" >&2

  help

  exit 1

fi

case $1 in

start)

  shift

  run "$@"

  ;;

stop)

  shift

  stop "$@"

  ;;

help)

  help

  exit 0

  ;;

esac