Automatic merge from submit-queue (batch tested with PRs 42486, 44780)

Hostname patch for vsphere provider limitations with juju

**What this PR does / why we need it**:
The Juju VSphere provider doesn't set a unique hostname which causes issues when scaling worker-pools and they all have the hostname `ubuntuguest`. Instead we assign the JUJU_UNIT_NAME to that hostname to prevent the collision which allows the master to sort out that there are multiple units and not one attempting re-registration.

**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/237

**Special notes for your reviewer**:
The charm-pre-exec runs before it installs the charm software so the validation can happen quickly. Check hostname output, as well as kubectl get no post deployment.


```release-note
Resolves juju vsphere hostname bug showing only a single node in a scaled node-pool.
```