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.
**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 --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 --timeout=1ms
Unable to connect to the server: net/http: request canceled while
waiting for connection (Client.Timeout exceeded while awaiting headers)
```
This changes clientcmd to skip the default cluster, but preserves the
behavior in kubectl. This prevents the possibility of an administrator
misconfiguration in kubelet or other server component from allowing a
third party who can bind to 8080 on that host from potentially
impersonating an API server and gaining root access.
