e2e: KEP-2033: test KubeletInUserNamespace

To verify:

```
dockerd-rootless-setuptool.sh install
kubetest2-kind --build --up --down --test=ginkgo -- --use-built-binaries  --focus-regex='\[Feature:KubeletInUserNamespace\]'
```

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>