How to produce an array of machine options with MACHINE_OPTIONS env variable ?

Summary

I'm looking how to produce an array of machine options with MACHINE_OPTIONS en variable

Steps to reproduce

$ docker run --name gitlab-ci-multi-runner --restart=always --env='CI_SERVER_URL=https://gitlab.com/ci' --env='RUNNER_NAME=test' --env='REGISTRATION_TOKEN=XXXXX' --env='RUNNER_EXECUTOR=docker+machine' --env='DOCKER_IMAGE=docker:latest' --env='MACHINE_OPTIONS=digitalocean-image=coreos-stable,digitalocean-ssh-user=core' gitlab/gitlab-runner
$ docker exec -ti gitlab-ci-multi-runner bash
root@f039702abecf:/# gitlab-runner register -n

Actual behavior

root@f039702abecf:/# cat /etc/gitlab-runner/config.toml
concurrent = 1
check_interval = 0

[[runners]]
  name = "test"
  url = "https://gitlab.com/ci"
  token = "XXXXX"
  executor = "docker+machine"
  [runners.docker]
    tls_verify = false
    image = "docker:latest"
    privileged = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0
  [runners.cache]
  [runners.machine]
    IdleCount = 0
    MachineDriver = ""
    MachineName = ""
    MachineOptions = ["digitalocean-image=coreos-stable,digitalocean-ssh-user=core"]
    OffPeakTimezone = ""
    OffPeakIdleCount = 0
    OffPeakIdleTime = 0

Expected behavior

We should have :

MachineOptions = ["digitalocean-image=coreos-stable","digitalocean-ssh-user=core"]

Instead of :

MachineOptions = ["digitalocean-image=coreos-stable,digitalocean-ssh-user=core"]

Used GitLab Runner version

root@f039702abecf:/# gitlab-runner --version
Version:      9.5.0
Git revision: 413da38
Git branch:   9-5-stable
GO version:   go1.8.3
Built:        Tue, 22 Aug 2017 13:35:13 +0000
OS/Arch:      linux/amd64
Edited by rockandska