revert data_changed guard on create_kubeconfig

[kwmonroe]

This partially reverts #33. @joedborg hit an issue where the k8s master would write kubeconfig before the kubeapi-load-balancer joined. This caused server: $master:6443 to be written to the config file. Since we weren't checking for server in data_changed's config_matrix, we never re-wrote an accurate config that included the load balancer's ip.

server isn't the only problem -- we would have also missed any changes to ca_crt and client_pass because the conf.read() happens before any of these changed values get written, which would make data_changed False and cause us to return early.

For now, we'll keep the part of #33 that logs the write to disk (versus a more expensive status_set on every hook).

To fully fix the spirit of https://bugs.launchpad.net/charm-kubernetes-master/+bug/1822021, we'll need to implement a helper that can compare what's on disk to what would be written to disk, and write a new config when the 2 differ.

[joedborg]

Looks good to me!