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Ensure /etc/hosts has a header always - Fix conformance test
**What this PR does / why we need it**:
We need to be able to tell if an /etc/hosts in a container has been touched by kubernetes or not (whether we use the host network or not).
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
ba20e63446 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.
**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#60938
**Special notes for your reviewer**:
Also see
- https://github.com/kubernetes/kubernetes/pull/61405
- https://github.com/kubernetes/kubernetes/pull/60939
- https://github.com/kubernetes/kubernetes/issues/60938
**Release note**:
```release-note
NONE
```
368233b9b8