make /var a runtime volume

[BenTheElder]

Per the Filesystem Hierarchy Standard all of /var is persistent runtime files. This should not be on the container filesystem.

Moving this to a runtime anonymous volume for all of /var:

• allows us to not put any /var/... volumes in the base image (for container runtime storage, which must not be stacked)
  • which will allow us to potentially add pre-loaded images to an existing node image
• ensures writes to anything in /var goes to a volume instead of the container filesystem

The only downside is that new kind images will require a new version of kind. Images built prior to this should continue to work even with the new version.

While doing this I also normalized on long flags for node creation for clarity and consistency.

[BenTheElder]

/hold
doing some debugging locally to make sure everything does what I want :-)

[BenTheElder]

/hold cancel

[BenTheElder]

this is recursive, and from upstream (difficult to find docs for this though...)
we don't know what mounts users will try to propagate, so everything is made shared

we need this change not just because it's more correct, but because /var/lib/containerd is no longer a mount point

[BenTheElder]

/retest
(prow failing to create the pod)

[amwat]

/lgtm
/approve

[k8s-ci-robot]

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