[Feature Request] configurable force_pull_image for the app_image

[lhoss]

Would be useful to support configuring the marathon' docker container field force_pull_image (and keep the default false).

This would require the field here , plus some more config handling code:

https://github.com/vigsterkr/marathonspawner/blob/master/marathonspawner/marathonspawner.py#L248
 def start(self):
        docker_container = MarathonDockerContainer(
            ...
            force_pull_image=self.force_pull_image,

[vigsterkr]

@lhoss sure thing if you can specify more what is required for you i can add it right away... one question though: are you using this internally? or what's the usecase? :) would be great if you could share

[lhoss]

@vigsterkr great to hear!
we plan to use Jupyter-Hub on our Mesos/Marathon platform, but no time yet to get really into it, so not sure yet what other features of marathon app configs would be nice.