Automatic merge from submit-queue (batch tested with PRs 49861, 50933, 51380, 50688, 51305)

Test loading Kubelet config from a file

**What this PR does / why we need it**:
Adds a test for loading kubelet config from a file, part of improving https://github.com/kubernetes/kubernetes/issues/50217

**Release note**:
```release-note
NONE
```