Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

juju: Make kubernetes-master status handling more robust

**What this PR does / why we need it**:

This fixes a charm hook failure that can occur after restarting kubernetes-master units in Juju-based Kubernetes deployments.

This should also hopefully make our status handling in kubernetes-master more robust in general, by making sure all of our `blocked`, `waiting`, and `active` status messages are handled in one place, on hook exit.

**Which issue(s) this PR fixes**:

https://github.com/juju-solutions/bundle-canonical-kubernetes/issues/523

**Release note**:

```release-note
NONE
```