Automatic merge from submit-queue (batch tested with PRs 48139, 48042, 47645, 48054, 48003)
Add a failsafe for etcd not returning a connection string
**What this PR does / why we need it**: Removing a kubernetes-master will fail as described on this issue: https://github.com/juju-solutions/bundle-canonical-kubernetes/issues/311
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes https://github.com/juju-solutions/bundle-canonical-kubernetes/issues/311
**Special notes for your reviewer**: This is a two liner defensive code. I am not totally sold on this patch. I might not be the right place to address the above issue. However, solving the problem on the etcd side and updating the interface scope to be unit (as suggested) seems much more involving.
**Release note**:
```
Fix error when removing juju kubernetes-master unit
```
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