Automatic merge from submit-queue
add suggestion to use `describe` to obtain container names
**Release note**:
```release-note
release-note-none
```
Commands with the `--container=` option provide no suggestions to a user
on how to obtain a container's name from a pod.
This patch adds a suggestion on the usage output to use the `describe`
command on a pod to obtain the container value that is passed to the
`--container=` flag.
`$ kubectl exec -h`
```
Execute a command in a container.
Examples:
kubectl exec 123456-7890 date
kubectl exec 123456-7890 -c ruby-container date
kubectl exec 123456-7890 -c ruby-container -i -t -- bash -il
Flags:
-c, --container string Container name. If omitted, the first container in the pod will be chosen. Use the 'describe' command to find the list of containers on a pod.
-p, --pod string Pod name
-i, --stdin Pass stdin to the container
-t, --tty Stdin is a TTY
f9e1ef97db