Flaky test: `when there are container env vars in files`

[aeijdenberg]

In spec/models/docker_manager_spec.rb, the when there are container env vars in files test is flaky.

On my system, the env variables list comes out in one particular order, such that I need to re-order the values in the test in order to pass. In your Travis config, they come out in a different order.

As far as I'm aware, there's isn't a defined order they should be in, so I would guess the test should be fixed to not care (maybe just sort both lists before comparing?).

I don't know enough Ruby to easily do so, so apologies for no attached PR.