kola: add kubeadm tests

[tormath1]

In this PR, we add kubernetes tests using kubeadm and ignition to setup the cluster.

A user-data script will be uploaded through ignition on both worker and controller in order to run the required commands. ignition will take care of pulling required binaries / uploading various files (user-data, manifest).

Test will assert that there is two running nodes and it will deploy a nginx pod.

How to use

./build kola

Testing done

It has been tested on qemu platform with alpha-2823.0.0:

$ sudo ./bin/kola run -b cl -p qemu --qemu-image flatcar_production_qemu_image.img kubeadm.base
=== RUN   kubeadm.base
=== RUN   kubeadm.base/node_readiness
=== RUN   kubeadm.base/nginx_deployment
--- PASS: kubeadm.base (317.05s)
        cluster.go:117: Created symlink /etc/systemd/system/multi-user.target.wants/kubelet.service → /etc/systemd/system/kubelet.service.
        cluster.go:117: 	[WARNING Service-Docker]: docker service is not enabled, please run 'systemctl enable docker.service'
        cluster.go:117: 	[WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
    --- PASS: kubeadm.base/node_readiness (52.85s)
    --- PASS: kubeadm.base/nginx_deployment (22.12s)
PASS, output in _kola_temp/qemu-2021-04-26-1847-14719

and on GCP with latest alpha (alpha-2857.0.0) (note --gce-machinetype=n1-standard-2):

./bin/kola run --basename=${BASENAME} \
    --gce-image=${IMAGE_NAME} \
    --gce-json-key=${GCE_JSON_KEY} \
    --parallel=4 --gce-machinetype=n1-standard-2 --platform=gce \
    ${TEST_NAME}
=== RUN   kubeadm.base
=== RUN   kubeadm.base/node_readiness
=== RUN   kubeadm.base/nginx_deployment
--- PASS: kubeadm.base (294.59s)
    --- PASS: kubeadm.base/node_readiness (25.84s)
    --- PASS: kubeadm.base/nginx_deployment (15.90s)
PASS, output in _kola_temp/gce-2021-04-30-1131-290038

What's missing

• try to use ignition instead of script to provision the nodes (worker and master)
• test on other platforms
• add some unit-tests maybe to test the logic
• decide what we should do: should we merge kubeadm and kubernetes tests ? should we drop the current kubernetes tests in favor of this one ? let's keep them in a separate test, then we will remove slowly the kubernetes ones

[tormath1]

@pothos comments have been addressed. Ignition is also now used to download binaries file and also to upload "user-data" and nginx manifest.

[tormath1]

@pothos thanks for the review - comments have been addressed !

[pothos]

Good to go, thanks!
In a follow up PR we can exclude problematic platforms if we see in the CI that some platforms do not work for whatever reason.