Generalize running_in_container function

[emalm]

This change allows jobs to run correctly in garden-runc containers
as well as in the previously supported garden-linux and docker containers.

[cfdreddbot]

Hey ematpl!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/136408735

The labels on this github issue will be updated when the story is started.

[jaresty]

@ematpl Can you explain a bit more what is going on here? This is the first time I've seen this code so I'm not sure of the best way to test that it is working properly.

• What did it used to do, and what is it doing now?
• What could be affected by this change, and how could I test that those things still function correctly?

Thanks for your help. Please feel free to stop by in person to demonstrate if it's easier than replying in a comment.

[emalm]

Thanks @ChunyiLyu and @jaresty ! Please let me know if you need any more information about the changes in this PR.

[ChunyiLyu]

@ematpl No worries! Jesse filled in the information about this PR. Our bosh-lite successfully deployed and CATs had passed as well. It all looks good :)

[emalm]

Awesome, thanks!