Automatic merge from submit-queue
Add not-running check to kubectl-exec
Different cases:
- pod is started, container terminated:
```
error: error executing remote command: error executing command in container: container not found ("sleep1")
```
- pod has terminated:
```
error: cannot exec into a container in a completed pod; current phase is Succeeded
```
- container does not exist in pod spec:
```
Error from server: container foo is not valid for pod multi-container
```
Fixes https://github.com/openshift/origin/issues/8472#event-681794952