cgroup names created by kubelet should be lowercased

[derekwaynecarr]

What this PR does / why we need it:
This PR modifies the kubelet to create cgroupfs names that are lowercased. This better aligns us with the naming convention for cgroups v2 and other cgroup managers in ecosystem (docker, systemd, etc.)

See: https://www.kernel.org/doc/Documentation/cgroup-v2.txt
"2-6-2. Avoid Name Collisions"

Special notes for your reviewer:
none

Release note:

kubelet created cgroups follow lowercase naming conventions

[derekwaynecarr]

/cc @vishh

[k8s-reviewable]

This change is 

[derekwaynecarr]

for reference, i believe future users will view our naming syntax confusing with its use of mixed case. as a result, i think this is a bug. there is no issue to reference, as users have not tried integrating or introspecting the cgroupfs yet.

[smarterclayton]

Agree this is a bug in that we are potentially causing problems in the future

[sjenning]

@derekwaynecarr i think this needs to be updated too

https://github.com/kubernetes/kubernetes/blob/master/test/e2e_node/pods_container_manager_test.go#L157

or here

https://github.com/kubernetes/kubernetes/blob/master/test/e2e_node/pods_container_manager_test.go#L64

[vishh]

One more option is to have cgroup manager default to lower case names. It might break tests though and could lead to confusion if the defaulting isn't obvious.

[vishh]

Will tag once the tests pass.

[derekwaynecarr]

everything but the cross build is happy due to node problem detector problems.

[vishh]

/lgtm

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

The following people have approved this PR: derekwaynecarr, vishh

Needs approval from an approver in each of these OWNERS Files:

• pkg/kubelet/OWNERS [derekwaynecarr,vishh]
• test/e2e_node/OWNERS [vishh]

We suggest the following people:
cc @timstclair
You can indicate your approval by writing /approve in a comment
You can cancel your approval by writing /approve cancel in a comment

[derekwaynecarr]

rebased, retagging.

[derekwaynecarr]

@k8s-bot kops aws e2e test this

[derekwaynecarr]

GCE failure is #42597

The other is a federation flake not impacted by this pr.

[derekwaynecarr]

@k8s-bot unit test this
@k8s-bot cvm gce e2e test this

[k8s-github-robot]

Automatic merge from submit-queue

[vishh]

Uff! Finally it's merged...

…

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