test/e2e_node/system/types_unix: support ZFS

[neolit123]

What this PR does / why we need it:

Docker validation tests in the case of ZFS used as the graph driver
fail due to "zfs" not being present in the default Docker specification.

Add "zfs" in the GraphDriver slice.

kubeadm relies on the DockerValidator and pre-flight checks would fail if the user is using ZFS.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Updates kubernetes/kubeadm#930

Special notes for your reviewer:
NONE

/cc @kubernetes/sig-node-pr-reviews
/cc @kubernetes/sig-cluster-lifecycle-pr-reviews
/cc @kvaps (reported by)
/area node-e2e
/area kubeadm

Release note:

Unix: support ZFS as a valid graph driver for Docker

[neolit123]

/test pull-kubernetes-e2e-gce

[luxas]

/lgtm
Needs approval by @kubernetes/sig-node-pr-reviews

[luxas]

/kind bug

[ConnorDoyle]

In general this seems fine. My only question is that since this system spec is also used in e2e_node_suite_test.go, whether this implies any particular level of support for docker + zfs.

cc @timothysc @derekwaynecarr

[neolit123]

my only confirmation that people are actually using ZFS + Docker + k8s is the issue report that triggered this PR:
kubernetes/kubeadm#930 (comment)

and also this blog post:
https://hackernoon.com/starting-small-with-kubernetes-and-kubeadm-500-containers-6c76454e6e12

so in a way people are already using it, but not sure how a particular level of support can be defined for a Docker graph driver.

[dashpole]

While we don't have any e2e testing to validate that ZFS works each release, there are definitely people using it. There is a group of contributors that submit bug-fixes for ZFS to cAdvisor, so I expect zfs to continue to function in future releases.

[ConnorDoyle]

The only supported Docker storage driver missing here is vfs which as IIUC isn't desirable in most production settings. If anyone needs that driver whitelisted in the default spec they can create a new issue.

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ConnorDoyle, luxas, neolit123

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[neolit123]

@ConnorDoyle @luxas
do you think i should cherry-pick this for older releases and which ones?

[k8s-github-robot]

Automatic merge from submit-queue (batch tested with PRs 65348, 65599, 65635, 65688, 65691). If you want to cherry-pick this change to another branch, please follow the instructions here.