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