Automatic merge from submit-queue (batch tested with PRs 50094, 48966, 49478, 50593, 49140)
Kubelet manage hosts file for HostNetwork Pods instead of Docker
**What this PR does / why we need it**: Currently, Docker manages the hosts file for containers inside Pods using hostNetwork. It creates discrepancy between how we treat hostNetwork and non-hostNetwork Pods. Kubelet should manage the file regardless of the network setup.
**Which issue this PR fixes**: fixes#48397 more context in https://github.com/kubernetes/kubernetes/issues/43632#issuecomment-304376441
**Special notes for your reviewer**: Because the new logic relies on reading the node filesystem, I'm not sure how to write a proper unit test. I was thinking about using a node e2e test to cover the case, but suggestions are greatly welcomed.
**Release note**:
```release-note
Kubelet now manages `/etc/hosts` file for both hostNetwork Pods and non-hostNetwork Pods.
```
/kind feature
/sig node
@yujuhong @hongchaodeng @thockin
@kubernetes/sig-network-feature-requests @kubernetes/sig-node-feature-requests
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