Honor KUBECONFIG environment variable

[tcassaert]

I'm using Kubie to switch between Kubernetes clusters. Right now it's impossible to combine KubeNodeUsage with Kubie as Kubie sets the KUBECONFIG environment variable and KubeNodeUsage is not honoring it and defaults to ~/.kube/config.

[AKSarav]

Thanks for letting me know @tcassaert - will solve this one soon