Automatic merge from submit-queue (batch tested with PRs 41061, 40888, 40664, 41020, 41085)
kubeadm: Small cleanup and fixes, validate the service subnet
**What this PR does / why we need it**:
- Validate the minimum subnet cidr so there are always 10 available addresses
- Remove an old proxy arg function, add clustercidr to the proxy manifest and automatically calculate the dns ip
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
@errordeveloper @pires @mikedanese @dmmcquay @dgoodwin
