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