Automatic merge from submit-queue.

Ensure /etc/hosts has a header always - Fix conformance test

We have 2 scenarios where we copy /etc/hosts
- with host network (we just copy the /etc/hosts from node)
- without host network (create a fresh /etc/hosts from pod info)

We are having trouble figuring out whether a /etc/hosts in a
pod/container has been "fixed-up" or not. And whether we used
host network or a fresh /etc/hosts in the various ways we start
up the tests which are:

- VM/box against a remote cluster
- As a container inside the k8s cluster
- DIND scenario in CI where test runs inside a managed container

Please see previous mis-guided attempt to fix this problem at
ba20e634 In this commit we revert
the code from there as well.

So we should make sure:
- we always add a header if we touched the file
- we add slightly different headers so we can figure out if we used the
  host network or not.

Update the test case to inject /etc/hosts from node to another path
(/etc/hosts-original) as well and use that to compare.



**What this PR does / why we need it**:

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
Rework Kubelet set `/etc/hosts` behavior to fix conformance testability
```