support kube_config exec

[cjhodges77]

Is there a plan to support the kube_config exec function? as in:

users:
- name: user-name
  user:
    exec:
      apiVersion: client.authentication.k8s.io/v1alpha1
      command: heptio-authenticator-aws
      args:

[motymichaely]

@cjhodges77 I needed this as well so I just implemented it ;)

[cben]

Closed by #363 (thanks Moty again).