Allow configuration from kubectl config file

[sebastien-prudhomme]

I find that the configuration of the provider or the cluster is not that easy.

It should be better to allow reusing kubectl config file for provider or cluster configuration:

• by default the filename is $HOME/.kube/config (should be a parameter)
• by default it uses the "current-context' in the config file (should be also a parameter)
• you can also override cluster and user names

See options in kubectl:

      --cluster='': The name of the kubeconfig cluster to use
      --context='': The name of the kubeconfig context to use
      --kubeconfig='': Path to the kubeconfig file to use for CLI requests.
      --user='': The name of the kubeconfig user to use