Automatic merge from submit-queue

Add 'kubectl set image'

```release-note
Add "kubectl set image" for easier updating container images (for pods or resources with pod templates). 
```

**Usage:**
```
kubectl set image (-f FILENAME | TYPE NAME) CONTAINER_NAME_1=CONTAINER_IMAGE_1 ... CONTAINER_NAME_N=CONTAINER_IMAGE_N
```
**Example:**
```console 
# Set a deployment's nginx container image to 'nginx:1.9.1', and its busybox container image to 'busybox'.
$ kubectl set image deployment/nginx busybox=busybox nginx=nginx:1.9.1

# Update all deployments' nginx container's image to 'nginx:1.9.1'
$ kubectl set image deployments nginx=nginx:1.9.1 --all

# Update image of all containers of daemonset abc to 'nginx:1.9.1'
$ kubectl set image daemonset abc *=nginx:1.9.1

# Print result (in yaml format) of updating nginx container image from local file, without hitting the server 
$ kubectl set image -f path/to/file.yaml nginx=nginx:1.9.1 --local -o yaml
```

I abandoned the `--container=xxx --image=xxx` flags in the [deploy proposal](https://github.com/kubernetes/kubernetes/blob/master/docs/proposals/deploy.md#kubectl-set) since it's much easier to use with just KEY=VALUE (CONTAINER_NAME=CONTAINER_IMAGE) pairs. 

Ref #21648 
@kubernetes/kubectl @bgrant0607 @kubernetes/sig-config 


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