Added load_config_file option to the provider k8s part

[meyskens]

Fixes #230

[rporres]

Shouldn’t this be feasible setting in_cluster to false? I mean, I like much more the load_config_file name, but I fail to see the difference between both or why we should keep both (when it would be useful, I mean)

We may want to deprecate in_cluster in favour of load_config_file so that we're in-sync with the k8s provider

[rporres]

The problem here is that in_cluster is kinda broken. It should avoid loading .kube/config as it should call kubernets InClusterConfig function: https://godoc.org/k8s.io/client-go/rest#InClusterConfig

There can be two situations why you don't want to load .kube/config

• You're running inside a pod and you want to authenticate using the service account k8s gives to pods
• You don't want it for your own personal reasons

Let's merge this as it is. I will update #68 to signal that it has still work to do