Automatic merge from submit-queue

Add global timeout flag

**Release note**:
```release-note
Add a new global option "--request-timeout" to the `kubectl` client
```

UPSTREAM: https://github.com/kubernetes/client-go/pull/10

This patch adds a global timeout flag (viewable with `kubectl -h`) with
a default value of `0s` (meaning no timeout).

The timeout value is added to the default http client, so that zero
values and default behavior are enforced by the client.

Adding a global timeout ensures that user-made scripts won't hang for an
indefinite amount of time while performing remote calls (right now, remote
calls are re-tried up to 10 times when each attempt fails, however, there is
no option to set a timeout in order to prevent any of these 10 attempts from
hanging indefinitely).

**Example**
```
$ kubectl get pods # no timeout flag set - default to 0s (which means no
timeout)
NAME                      READY     STATUS    RESTARTS   AGE
docker-registry-1-h7etw   1/1       Running   1          2h
router-1-uv0f9            1/1       Running   1          2h

$ kubectl get pods --request-timeout=0 # zero means no timeout no timeout flag set
NAME                      READY     STATUS    RESTARTS   AGE
docker-registry-1-h7etw   1/1       Running   1          2h
router-1-uv0f9            1/1       Running   1          2h

$kubectl get pods --request-timeout=1ms
Unable to connect to the server: net/http: request canceled while
waiting for connection (Client.Timeout exceeded while awaiting headers)
```