consider support stacked kubeconfig environment

[Dentrax]

What steps did you take:

$ sudo -E kwt net start

What happened:

Error: Building Kubernetes config: stat :/Users/furkan.turkal/.kube/config:/Users/furkan.turkal/.kube/config-aws:/Users/furkan.turkal/.kube/config-gcloud:/Users/furkan.turkal/.kube/config-local: no such file or directory

What did you expect:
It should parse stacked-kubeconfigs?

Anything else you would like to add:

$ echo $KUBECONFIG
:/Users/furkan.turkal/.kube/config:/Users/furkan.turkal/.kube/config-aws:/Users/furkan.turkal/.kube/config-gcloud:/Users/furkan.turkal/.kube/config-local

The following one works like a charm!

KUBECONFIG=/Users/furkan.turkal/.kube/config sudo -E kwt net start

Environment:

• kwt version (execute kwt version): Client Version: 0.0.6

This is just a low-priority issue, dropping here, so we don't forget. Thanks.