fix: launching from local images in kubernetes

[th7nder]

When launching using Kubernetes provider (zombienet -p kubernetes) and using minikube, I needed to use local image without publishing it.
I can add it to minikube, by using minikube image load image-name:tag and specify in zombienet.toml:

[settings]
image_pull_policy = "IfNotPresent"

However, it'd still fail at the creating bootnodes (and running --help commands), because the policy was to Always download images and they were not published.

Ideally, this option probably should be sourced from networkSpec.settings.image_pull_policy, but I left it at this level.

Let me know what you think!

Sort of related to #1829 (as a workaround to not having private registries)

[cla-bot-2021]

User @th7nder, please sign the CLA here.

[pepoviola]

Hi @th7nder, thanks for the feedback. Yes, those pods should read the config from the settings in order to behave like the rest. I can make those changes to fix this.

Thanks!