Automatic merge from submit-queue
Fix system container detection in kubelet on systemd
```release-note
Fix system container detection in kubelet on systemd.
This fixed environments where CPU and Memory Accounting were not enabled on the unit
that launched the kubelet or docker from reporting the root cgroup when
monitoring usage stats for those components.
```
Fixes https://github.com/kubernetes/kubernetes/issues/25909
/cc @kubernetes/sig-node @kubernetes/rh-cluster-infra @vishh @dchen1107
Check docker's pid file, then fallback to pidof when trying to determine the pid for docker. The
latest docker RPM for RHEL changes /usr/bin/docker from an executable to a shell script (to support
/usr/bin/docker-current and /usr/bin/docker-latest). The pidof check for docker fails in this case,
so we check /var/run/docker.pid first (the default location), and fallback to pidof if that fails.
`--kubelet-cgroups` and `--system-cgroups` respectively.
Updated `--runtime-container` to `--runtime-cgroups`.
Cleaned up most of the kubelet code that consumes these flags to match
the flag name changes.
Signed-off-by: Vishnu kannan <vishnuk@google.com>
