kubeconfig file is written for every hook

[Kevin W Monroe]

This is a follow-up to:

https://bugs.launchpad.net/charm-kubernetes-master/+bug/1822021

We call build_kubeconfig every time certs and auth are available (which is every hook once the cluster is up). The initial fix guarded the write with a data_changed, but that proved problematic because we weren't catching important fields that were changing:

https://github.com/charmed-kubernetes/charm-kubernetes-master/pull/41

We *could* re-implement that and add all the config opts that we care about (server, ca, pass, ks, etc), but that's awfully easy to miss a future config value. It's better to write an accurate config every hook than to miss a write when config changed.

We could also implement a "generate_kubeconfig" helper that would spit out what the config will look like, compare that to what's on disk, and write when the 2 differ.

[Cory Johns (johnsca)]

https://github.com/charmed-kubernetes/layer-kubernetes-common/pull/17

[Cory Johns (johnsca)]

Backported to stable in https://github.com/charmed-kubernetes/layer-kubernetes-common/commit/319771fef29b4523c975fb7dd0dfb378610e2108

[Cory Johns (johnsca)]

This was released on May 28th with bundle rev 679 / kubernetes-master rev 1008.