Some storage tests deploy DaemonSets which hard-code /var/lib/kubelet as root
directory for kubelet registration and pod directory. There was already a
parameter which allowed specifying the root directory, just with a very
confusing name ("--volume-dir") and matching field name. A --kubelet-root-dir
parameters gets added because this may make it easier to find the parameter,
with the old name preserved as an alias for the same field for backwards
compatibility.
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