Automatic merge from submit-queue (batch tested with PRs 42024, 42780, 42808, 42640)

Handle NPD during cluster upgrade.

Generate NPD token during upgrade.

I could not fully verify this change because of https://github.com/kubernetes/kubernetes/issues/42199. However, at least I tried upgrade master, and the corresponding environment variables are correctly generated.
```
...
ENABLE_NODE_PROBLEM_DETECTOR: 'standalone'
...
KUBELET_TOKEN: 'PKNgAaVXeL3VojND2s0KMleELjzGK0oW'
```

@maisem @dchen1107