Automatic merge from submit-queue (batch tested with PRs 48317, 48313, 48351, 48357, 48115)

Ensure get_password is accessing a file that exists.

**What this PR does / why we need it**: get_password will throw an exception instead of returning None in case the basic_auth.csv file is missing but /root/cdk/ is there in a juju deployment.

**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/324

**Special notes for your reviewer**:

**Release note**:

```
Fix race condition where /root/cdk is not yet initialised in kubernetes-master setup by Juju  
```