Automatic merge from submit-queue
Automatically add node labels beta.kubernetes.io/{os,arch}
Proposal: #17981
As discussed in #22623:
> @davidopp: #9044 says cloud provider but can also cover platform stuff.
Adds a label `beta.kubernetes.io/platform` to `kubelet` that informs about the os/arch it's running on.
Makes it easy to specify `nodeSelectors` for different arches in multi-arch clusters.
```console
$ kubectl get no --show-labels
NAME STATUS AGE LABELS
127.0.0.1 Ready 1m beta.kubernetes.io/platform=linux-amd64,kubernetes.io/hostname=127.0.0.1
$ kubectl describe no
Name: 127.0.0.1
Labels: beta.kubernetes.io/platform=linux-amd64,kubernetes.io/hostname=127.0.0.1
CreationTimestamp: Thu, 31 Mar 2016 20:39:15 +0300
```
@davidopp @vishh @fgrzadkowski @thockin @wojtek-t @ixdy @bgrant0607 @dchen1107 @preillyme
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