kubelet: specify --containerd flag to specify containerd socket path

[etungsten]

Issue number:
Partially addresses #867

Description of changes:
We changed the containerd socket path to be /run/dockershim.sock in #796. cAdvisor assumes the containerd socket to be located at /run/containerd/containerd.sock.

Pass --containerd to kubelet to specify containerd socket path so cAdvisor can make calls to containerd for gathering metric metadata information.

Testing done:
Built bottlerocket image, ran in an EKS 1.15 cluster. Kubelet starts up fine, mark-successful-boot.service is OK. Node registers with the cluster successfully, pods run fine.
Most metrics now have metadata information, whereas before none of the metrics had any metadata information.

...
container_cpu_usage_seconds_total{container="kube-proxy",container_name="kube-proxy",cpu="total",id="/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-podf4bc1d43_e098_4f73_885e_36d6a678d0f3.slice/cri-containerd-c16e87d1b666e2909bebe42db582087b1f1edd2613535eeee0c49ca09a09e8f7.scope",image="sha256:f107a8632d08a7d7061a07b7110d630d4917856070ddd3136828da976ba51c7c",name="c16e87d1b666e2909bebe42db582087b1f1edd2613535eeee0c49ca09a09e8f7",namespace="kube-system",pod="kube-proxy-5hbpb",pod_name="kube-proxy-5hbpb"} 0.401646411 1585002411967
container_cpu_usage_seconds_total{container="kube-rbac-proxy",container_name="kube-rbac-proxy",cpu="total",id="/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-podcd9426e7_bc4b_4616_bbf9_5562beed33e0.slice/cri-containerd-b68c12ffba18588b822956a2c496bada9f9b475783921d3bffeec9ca78137185.scope",image="sha256:685a73a3c754b9c143e9c91c4e7a7989c4be667707d4c1ec67acc8eb917bd749",name="b68c12ffba18588b822956a2c496bada9f9b475783921d3bffeec9ca78137185",namespace="monitoring",pod="node-exporter-kqzz2",pod_name="node-exporter-kqzz2"} 0.522531731 1585002414645
container_cpu_usage_seconds_total{container="node-exporter",container_name="node-exporter",cpu="total",id="/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-podcd9426e7_bc4b_4616_bbf9_5562beed33e0.slice/cri-containerd-463e72e5406d8cd4ebbd64963a0b64ae803d7d339a3de124d7ce48ce27af3b98.scope",image="quay.io/prometheus/node-exporter:v0.18.1",name="463e72e5406d8cd4ebbd64963a0b64ae803d7d339a3de124d7ce48ce27af3b98",namespace="monitoring",pod="node-exporter-kqzz2",pod_name="node-exporter-kqzz2"} 0.143221556 1585002414216
...

Note that some metrics are still missing metadata information, e.g. most filesystem related metrics have missing metadata information.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[zmrow]

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