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)
```
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