Remove --skip-preflight-checks, ignore unwanted checks

[afbjorklund]

Better to ignore the checks that we don't want, rather than
disabling all of them in case something important appears...

Currently known failing checks:
[WARNING SystemVerification]: docker version is greater than
the most recently validated version. Docker version: 17.06.0-ce. Max validated version: 17.03
[WARNING FileExisting-crictl]: crictl not found in system path
[WARNING Service-Docker]: docker service is not enabled, please run 'systemctl enable docker.service'
[ERROR DirAvailable--etc-kubernetes-manifests]: /etc/kubernetes/manifests is not empty
[ERROR Swap]: running with swap on is not supported. Please disable swap

---

https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.9.md

The kubeadm --skip-preflight-checks flag is now deprecated and will be removed in a future release.

[afbjorklund]

crictl was added as: #2404

[minikube-bot]

Can one of the admins verify this patch?

[dlorenc]

@minikube-bot ok to test

[afbjorklund]

The systemd files were removed in 56e250e, since it needs runtime configuration. But it could probably "enable" the needed runtime, if that makes kubeadm happy.

sudo systemctl daemon-reload &&
sudo systemctl enable kubelet &&
sudo systemctl enable $RUNTIME &&
sudo systemctl start kubelet

Where $RUNTIME would be the same as kubelet.service, maybe docker.service instead of docker.socket:

[Install]
{{if or (eq .ContainerRuntime "cri-o") (eq .ContainerRuntime "cri")}}Wants=crio.service{{else}}Wants=docker.socket{{end}}

Since: docker.socket depends on docker.service, but kubeadm only checks docker.service.

[afbjorklund]

Swap is discussed in #1827

[afbjorklund]

Service enabled in: #2406

[afbjorklund]

1.9.1 says:
Flag --skip-preflight-checks has been deprecated, it is now equivalent to --ignore-preflight-errors=all

[dlorenc]

Is this ready to be merged?

[afbjorklund]

@dlorenc : I think so, it should handle all errors. The warnings however, are addressed in separate PRs

[dlorenc]

@minikube-bot test this please